Numerical control oscillator, digital frequency converter and radio frequency unit

ABSTRACT

A numerical control oscillator (NCO) for reducing a circuit size and power consumption while maintaining a desired frequency deviation, and suppressing generation of a spurious as much as possible. The NCO comprises a phase accumulator for accumulating input phase difference data to generate phase data, and a read only memory (ROM) for storing a phase/amplitude conversion table to output amplitude data corresponding to the phase data generated by the phase accumulator. The phase accumulator includes a phase register and a phase calculator. If a sampling frequency of an output signal from the NCO is Fs, the upper limit of a desired frequency setting interval of the output signal is FD and K and L are arbitrary integers, the phase calculator adds or subtracts the input phase difference data and phase data from the phase register to or from each other by a modulo operation taking the nearest integer of M as a modulus, where M=Fs/FD×K/L. The ROM has its address terminal connected to an output terminal of the phase accumulator. On the basis of the stored phase/amplitude conversion table, the ROM outputs amplitude data corresponding to phase data, input from the phase accumulator to the address terminal, through its data terminal as an output signal of the NCO set to a frequency setting interval of a dF step, where dF=FD/K×L.

PRIORITY

[0001] This application claims priority under 35 U.S.C. § 119 to anapplication entitled “Numerical Control Oscillator, Digital frequencyConverter and Radio Frequency Unit” filed in the Japanese IntellectualProperty Office on Dec. 11, 2002 and assigned Serial No. 359773/2002,the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a numerical control oscillatorfor frequency-converting a received signal into a demodulator inputsignal through a digital signal process, and a digital frequencyconverter and radio frequency unit including the same.

[0004] 2. Description of the Related Art

[0005] A conventional numerical control oscillator (NCO) includes aphase data accumulator, and a memory (for example, a read only memory(ROM)) for outputting sine data corresponding to a phase calculated bythe accumulator. Further, the NCO provides an output frequency definedas follows in Equation (1):

F=(Fs×R)/2^(j)  (1)

[0006] where, F is the output frequency, j is a phase word length, Fs isa sampling frequency, and R is an arbitrary integer.

[0007] In the case where a target frequency is obtained using a directdigital synthesizer (DDS) that digital/analog-converts and outputs anoutput signal from the NCO, the output frequency of the NCO can bechanged at a 200 KHz step by adjusting the sampling frequency of theoutput signal from the NCO to 200 KHz×2^(j) or extending the phase wordlength j (increasing the number of bits) to enhance a phase resolution,or frequency resolution, so that the difference between the targetfrequency and the output frequency of the NCO is within a range of anallowable deviation

[0008] For example, provided that the sampling frequency Fs is set to153.6 MHz in a system where the output frequency F is 1.92 GHz and theallowable output frequency deviation Δf is taken at a degree ofprecision of 0.1 ppm, the phase word length j will be taken as followsin Equation (2): $\begin{matrix}\begin{matrix}{j = {\log_{2}\left( {{{Fs}/\Delta}\quad f} \right)}} \\{= {\log_{2}\left( {153.6 \times {10^{6}/\left( {1.92 \times 10^{9} \times 0.1 \times 10^{- 6}} \right)}} \right)}} \\{\approx 19.61}\end{matrix} & (2)\end{matrix}$

[0009] It can be seen from the above Equation (2) that 20 bits arerequired to define the target phase word length j.

[0010] However, in the case where the phase word length j is extended,it is necessary to make the phase word length j equal to a word length kof the memory (the number of address bits of the memory) (j=k) in orderto obtain an output signal of the NCO with no spurious effects caused bytruncation of phase data. In the case of making the phase word length jlarger than the memory word length k (j>k) in order to suppress anincrease in memory size, it is necessary to requantize an address wordlength (memory word length) output from a phase calculator. Thisrequantization causes the occurrence of an error e^(p) of periodicity,which appears as a spurious in the output signal of the NCO (see Henry TNicholas, III and Henry Samueli, “An Analysis of the Output Spectrum ofDirect Digital Frequency Synthesizers in the Phase-AccumulatorTruncation” in Proc. Annual Frequency Control Symposium, 1987, pp495-502 (reference 1), for example).

[0011] On the other hand, known as a method for suppressing the spuriousresulting from the requantization of the address word length from thephase calculator is, for example, a method based on an error feedback orerror spread by design (see Jouko Vankka, “Spur. Reduction Techniques inSine Output Direct Digital Synthesis” in IEEE International FrequencyControl Symposium, 1996, pp 951-959 (reference 2), for example).However, as disclosed in reference 1, although the spurious is generatedin the output signal due to the requantization of the address wordlength from the phase calculator, the phase word length j inevitablybecomes larger than the memory word length k in order to suppress anincrease in memory size.

[0012] Further, the techniques disclosed in reference 2 aredisadvantageous in that additional circuits are required besides theoriginal target circuits, resulting in an increase in circuit size eventhough the memory size is not increased. The method for suppressing thespurious using the error spread by design involves an increase in noiselevel (noise floor), so it is not necessarily effective.

[0013] Moreover, setting the sampling frequency to 2^(j) times a desiredfrequency step makes it difficult to generate a reference frequency.

SUMMARY OF THE INVENTION

[0014] Therefore, the present invention has been designed in view of theabove and other problems, and it is an object of the present inventionto provide a numerical control oscillator for reducing a circuit sizeand power consumption while maintaining a desired frequency deviation,and suppressing generation of a spurious effects as much as possible,and a digital frequency converter and radio frequency unit including thesame.

[0015] In accordance with a first aspect of the present invention, theabove and other objects can be accomplished by a numerical controloscillator (NCO) comprising: a phase accumulator for accumulating inputphase difference data to generate phase data, the phase accumulatorincluding a register for storing and outputting the phase data, and acalculator for adding or subtracting the input phase difference data andthe phase data from the register to or from each other; and a memory forstoring a phase/amplitude conversion table to output amplitude datacorresponding to the phase data generated by the phase accumulator, theNCO being adapted to output a signal of a sampling frequency Fs,wherein: if an upper limit of a desired frequency setting interval of anoutput signal is FD and K and L are arbitrary integers, the calculatorof the phase accumulator is adapted to add or subtract the input phasedifference data and the phase data from the register to or from eachother by a modulo operation taking a nearest integer of M as a modulus,where M=Fs/FD×K/L; and the phase/amplitude conversion table is adaptedto output a signal set to a frequency setting interval of a dF step,where dF=FD/K×L.

[0016] In the NCO with the above-described configuration, if thesampling frequency of the output signal from the NCO is Fs, the upperlimit of the desired frequency setting interval of the output signal isFD and K and L are arbitrary integers, the phase/amplitude conversiontable includes M (integral M, where M=Fs/FD×K/L) amplitude data, and thephase accumulator generates phase data by accumulatively adding orsubtracting the input phase difference data by a modulo operation takingthe integral M as a modulus, and outputs the generated phase data as anaddress input to the phase/amplitude conversion table. As a result, thephase/amplitude conversion table outputs amplitude data corresponding tothe input phase data as an output signal of the NCO set to the frequencysetting interval of the dF step, where dF=FD/K×L.

[0017] In accordance with a second aspect of the present invention,there is provided a digital down-converter comprising a frequencyconverter including the NCO of the first aspect as a local oscillatorand serving to frequency-convert an input signal sampled at the samplingfrequency Fs, the digital down-converter converting and outputting theinput signal into an output signal with a frequency lower than that ofthe input signal, wherein, if a desired frequency setting interval ofthe input signal is FD and K and L are arbitrary integers, the frequencyconverter is adapted to frequency-convert the input signal using aspecific signal output from the local oscillator and set to a frequencysetting interval of a dF step, where dF=FD/K×L, the local oscillatoroutputting the specific signal by accumulating the phase difference databy a modulo operation taking a nearest integer of M as a modulus, whereM=Fs/FD×K/L.

[0018] In the digital down-converter with the above-describedconfiguration, in order to convert and output the input signal sampledat the sampling frequency Fs into an output signal with a frequencylower than that of the input signal, if the desired frequency settinginterval of the input signal is FD and K and L are arbitrary integers,the frequency converter frequency-converts the input signal using afrequency signal output from the NCO of the first aspect as the localoscillator and set to the frequency setting interval of the dF step,where dF=FD/K×L. In the case where the desired frequency settinginterval FD of the input signal is higher than or equal to the frequencysetting interval dF of the frequency converter and is evenly divisibleby it, the digital down-converter can convert the frequency of the inputsignal input thereto at the frequency setting interval FD into a desiredfrequency within the range of an allowable frequency deviation.

[0019] In accordance with a third aspect of the present invention, thereis provided a digital down-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal sampled at asampling frequency Fs1, and a second frequency converter including theNCO of the first aspect as a second local oscillator and serving tosecondarily frequency-convert an output signal from the first frequencyconverter, the digital down-converter converting and outputting theinput signal into an output signal with a frequency lower than that ofthe input signal by two frequency conversions, wherein: if a desiredfrequency setting interval of the input signal is FD and K1, K2 and L1are arbitrary integers, the first frequency converter is adapted tofrequency-convert the input signal using a first specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1×L1, the first local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1/L1; and the second frequency converter isadapted to, if a sampling frequency of the output signal from the firstfrequency converter is Fs2, frequency-convert the output signal from thefirst frequency converter using a second specific signal output from thesecond local oscillator and set to a frequency setting interval of anFD2 step, where FD2=(FD mod FD1)/K2, the second local oscillatoroutputting the second specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/(FD mod FD1)×K2.

[0020] The digital down-converter with the above-described configurationconverts and outputs the input signal sampled at the sampling frequencyFs1 into an output signal with a frequency lower than that of the inputsignal by two frequency conversions. If the desired frequency settinginterval of the input signal is FD, K1, K2 and L1 are arbitrary integersand the frequency setting interval FD is above the frequency settinginterval FD1 of the first frequency converter and is indivisible by it,the frequency deviation of the output signal from the digitaldown-converter will exceed an allowable range. For this reason, first,the first frequency converter frequency-converts the input signal usinga frequency signal output from the NCO of the first aspect as the firstlocal oscillator and set to the frequency setting interval of the FD1step, where FD1=FD/K1×L1. Then, the second frequency convertersecondarily frequency-converts the output signal from the firstfrequency converter using a frequency signal output from the NCO of thefirst aspect as the second local oscillator and set to the frequencysetting interval of the FD2 step, where FD2=(FD mod FD1)/K2. Therefore,the digital down-converter can convert the frequency of the input signalinput thereto at the frequency setting interval FD into a desiredfrequency within the range of an allowable frequency deviation.

[0021] In accordance with a fourth aspect of the present invention,there is provided a digital down-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal sampled at asampling frequency Fs1, and a second frequency including the NCO of thefirst aspect as a second local oscillator and serving to secondarilyfrequency-convert an output signal from the first frequency converter,the digital down-converter converting and outputting the input signalinto an output signal with a frequency lower than that of the inputsignal by two frequency conversions, wherein: if a desired frequencysetting interval of the input signal is FD and K1, K2 and L1 arearbitrary integers, the first frequency converter is adapted tofrequency-convert the input signal using a first specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1×L1, the first local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1/L1; and the second frequency converter isadapted to, if a sampling frequency of the output signal from the firstfrequency converter is Fs2, frequency-convert the output signal from thefirst frequency converter using a second specific signal output from thesecond local oscillator and set to a frequency setting interval of anFD2 step, where FD2=(FD1 mod FD)/K2, the second local oscillatoroutputting the second specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/(FD1 mod FD)×K2.

[0022] The digital down-converter with the above-described configurationconverts and outputs the input signal sampled at the sampling frequencyFs1 into an output signal with a frequency lower than that of the inputsignal by two frequency conversions. If the desired frequency settinginterval of the input signal is FD, K1, K2 and L1 are arbitrary integersand the frequency setting interval FD is below the frequency settinginterval FD1 of the first frequency converter and FD1 is indivisible byFD, the frequency deviation of the output signal from the digitaldown-converter will exceed an allowable range. For this reason, first,the first frequency converter frequency-converts the input signal usinga frequency signal output from the NCO of the first aspect as the firstlocal oscillator and set to the frequency setting interval of the FD1step, where FD1=FD/K1×L1. Then, the second frequency convertersecondarily frequency-converts the output signal from the firstfrequency converter using a frequency signal output from the NCO of thefirst aspect as the second local oscillator and set to the frequencysetting interval of the FD2 step, where FD2=(FD1 mod FD)/K2. Therefore,the digital down-converter can convert the frequency of the input signalinput thereto at the frequency setting interval FD into a desiredfrequency within the range of an allowable frequency deviation.

[0023] In accordance with a fifth aspect of the present invention, thereis provided a digital down-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal sampled at asampling frequency Fs1, and a second frequency converter including theNCO of the first aspect as a second local oscillator and serving tosecondarily frequency-convert an output signal from the first frequencyconverter, the digital down-converter converting and outputting theinput signal into an output signal with a frequency lower than that ofthe input signal by two frequency conversions, wherein: if a desiredfrequency setting interval of the input signal is FD and K1, K2 and L1are arbitrary integers, the first frequency converter is adapted tofrequency-convert the input signal using a first specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1×L1, the first local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1/L1; and the second frequency converter isadapted to, if a sampling frequency of the output signal from the firstfrequency converter is Fs2, frequency-convert the output signal from thefirst frequency converter using a second specific signal output from thesecond local oscillator and set to a frequency setting interval of anFD2 step, where FD2=FD/K2, the second local oscillator outputting thesecond specific signal by accumulating the phase difference data by amodulo operation taking a nearest integer of M2 as a modulus, whereM2=Fs2/FD×K2.

[0024] The digital down-converter with the above-described configurationconverts and outputs the input signal sampled at the sampling frequencyFs1 into an output signal with a frequency lower than that of the inputsignal by two frequency conversions. If the desired frequency settinginterval of the input signal is FD, K1, K2 and L1 are arbitraryintegers, and the frequency setting interval FD is higher than or equalto the frequency setting interval FD1 of the first frequency converterand is evenly divisible by it, or FD is lower than FD1 and FD1 is evenlydivisible by FD, first, the first frequency converter frequency-convertsthe input signal using a frequency signal output from the NCO of thefirst aspect as the first local oscillator and set to the frequencysetting interval of the FD1 step, where FD1=FD/K1×L1. Then, the secondfrequency converter secondarily frequency-converts the output signalfrom the first frequency converter using a frequency signal output fromthe NCO of the first aspect as the second local oscillator and set tothe frequency setting interval of the FD2 step, where FD2=FD/K2.Therefore, the digital down-converter can convert the frequency of theinput signal input thereto at the frequency setting interval FD into adesired frequency within the range of an allowable frequency deviation.

[0025] Preferably, in the digital down-converter of the third, fourth,or fifth aspect, the second frequency converter may stop its frequencyconversion.

[0026] In the case where a multiple of the frequency setting intervalFD1 of the first frequency converter is equal to that of the frequencysetting interval FD of the input signal, the digital down-converter withthe above-described configuration can convert the frequency of the inputsignal input thereto at the frequency setting interval FD into a desiredfrequency within the range of an allowable frequency deviation by meansof only the first frequency converter.

[0027] In accordance with a sixth aspect of the present invention, thereis provided a digital up-converter comprising a frequency converterincluding the NCO of the first aspect as a local oscillator and servingto frequency-convert an input signal, the digital up-converterconverting the input signal into a signal with a frequency higher thanthat of the input signal and outputting the converted signal as anoutput signal sampled at the sampling frequency Fs, wherein, if adesired frequency setting interval of the output signal is FD and K andL are arbitrary integers, the frequency converter is adapted tofrequency-convert the input signal using a specific signal output fromthe local oscillator and set to a frequency setting interval of a dFstep, where dF=FD/K×L, the local oscillator outputting the specificsignal by accumulating the phase difference data by a modulo operationtaking a nearest integer of M as a modulus, where M=Fs/FD×K/L.

[0028] In the digital up-converter with the above-describedconfiguration, in order to convert the input signal into a signal with afrequency higher than that of the input signal and output the convertedsignal as an output signal sampled at the sampling frequency Fs, if thedesired frequency setting interval of the output signal is FD and K andL are arbitrary integers, the frequency converter frequency-converts theinput signal using a frequency signal output from the NCO of the firstaspect as the local oscillator and set to the frequency setting intervalof the dF step, where dF=FD/K×L. In the case where the desired frequencysetting interval FD of the output signal is higher than or equal to thefrequency setting interval dF of the frequency converter and is evenlydivisible by it, the digital up-converter can set the frequency settinginterval of its output signal to FD.

[0029] In accordance with a seventh aspect of the present invention,there is provided a digital up-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal, and asecond frequency converter including the NCO of the first aspect as asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, the digitalup-converter performing two frequency conversions to convert the inputsignal into a signal with a frequency higher than that of the inputsignal and output the converted signal as an output signal sampled at asampling frequency Fs2, wherein: if a desired frequency setting intervalof the output signal is FD and K1, K2 and L2 are arbitrary integers, thesecond frequency converter is adapted to frequency-convert the outputsignal from the first frequency converter using a first specific signaloutput from the second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2×L2, the second local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/FD×K2/L2; and the first frequency converter isadapted to, if a sampling frequency of the input signal is Fs1,frequency-convert the input signal using a second specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=(FD mod FD2)/K1, the first local oscillatoroutputting the second specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/(FD mod FD2)×K1.

[0030] The digital up-converter with the above-described configurationperforms two frequency conversions to convert the input signal into asignal with a frequency higher than that of the input signal and outputthe converted signal as an output signal sampled at the samplingfrequency Fs2. If the desired frequency setting interval of the outputsignal is FD, K1, K2 and L2 are arbitrary integers and the frequencysetting interval FD is above the frequency setting interval FD2 of thesecond frequency converter and is indivisible by it, the frequencydeviation of the output signal from the digital up-converter will exceedan allowable range. For this reason, first, the first frequencyconverter frequency-converts the input signal using a frequency signaloutput from the NCO of the first aspect as the first local oscillatorand set to the frequency setting interval of the FD1 step, where FD1=(FDmod FD2)/K1. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the NCO of the first aspect as thesecond local oscillator and set to the frequency setting interval of theFD2 step, where FD2=FD/K2×L2. Therefore, the digital up-converter canset the frequency setting interval of its output signal to FD.

[0031] In accordance with an eighth aspect of the present invention,there is provided a digital up-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal, and asecond frequency converter including the NCO of the first aspect as asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, the digitalup-converter performing two frequency conversions to convert the inputsignal into a signal with a frequency higher than that of the inputsignal and output the converted signal as an output signal sampled at asampling frequency Fs2, wherein: if a desired frequency setting intervalof the output signal is FD and K1, K2 and L2 are arbitrary integers, thesecond frequency converter is adapted to frequency-convert the outputsignal from the first frequency converter using a first specific signaloutput from the second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2×L2, the second local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/FD×K2/L2; and the first frequency converter isadapted to, if a sampling frequency of the input signal is Fs1,frequency-convert the input signal using a second specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=(FD2 mod FD)/K1, the first local oscillatoroutputting the second specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/(FD2 mod FD)×K1.

[0032] The digital up-converter with the above-described configurationperforms two frequency conversions to convert the input signal into asignal with a frequency higher than that of the input signal and outputthe converted signal as an output signal sampled at the samplingfrequency Fs2. If the desired frequency setting interval of the outputsignal is FD, K1, K2 and L2 are arbitrary integers and the frequencysetting interval FD is below the frequency setting interval FD2 of thesecond frequency converter and FD2 is indivisible by FD, the frequencydeviation of the output signal from the digital up-converter will exceedan allowable range. For this reason, first, the first frequencyconverter frequency-converts the input signal using a frequency signaloutput from the NCO of the first aspect as the first local oscillatorand set to the frequency setting interval of the FD1 step, whereFD1=(FD2 mod FD)/K1. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the NCO of the first aspect as thesecond local oscillator and set to the frequency setting interval of theFD2 step, where FD2=FD/K2×L2. Therefore, the digital up-converter canset the frequency setting interval of its output signal to FD.

[0033] In accordance with a ninth aspect of the present invention, thereis provided a digital up-converter comprising a first frequencyconverter including the NCO of the first aspect as a first localoscillator and serving to frequency-convert an input signal, and asecond frequency converter including the NCO of the first aspect as asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, the digitalup-converter performing two frequency conversions to convert the inputsignal into a signal with a frequency higher than that of the inputsignal and output the converted signal as an output signal sampled at asampling frequency Fs2, wherein: if a desired frequency setting intervalof the output signal is FD and K1, K2 and L2 are arbitrary integers, thesecond frequency converter is adapted to frequency-convert the outputsignal from the first frequency converter using a first specific signaloutput from the second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2×L2, the second local oscillatoroutputting the first specific signal by accumulating the phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/FD×K2/L2; and the first frequency converter isadapted to, if a sampling frequency of the input signal is Fs1,frequency-convert the input signal using a second specific signal outputfrom the first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1, the first local oscillator outputtingthe second specific signal by accumulating the phase difference data bya modulo operation taking a nearest integer of M1 as a modulus, whereM1=Fs1/FD×K1.

[0034] The digital up-converter with the above-described configurationperforms two frequency conversions to convert the input signal into asignal with a frequency higher than that of the input signal and outputthe converted signal as an output signal sampled at the samplingfrequency Fs2. If the desired frequency setting interval of the outputsignal is FD, K1, K2 and L2 are arbitrary integers, and the frequencysetting interval FD is higher than or equal to the frequency settinginterval FD2 of the second frequency converter and is evenly divisibleby it, or FD is lower than FD2 and FD2 is evenly divisible by FD, first,the first frequency converter frequency-converts the input signal usinga frequency signal output from the NCO of the first aspect as the firstlocal oscillator and set to the frequency setting interval of the FD1step, where FD1=FD/K1. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the NCO of the first aspect as thesecond local oscillator and set to the frequency setting interval of theFD2 step, where FD2=FD/K2×L2. Therefore, the digital up-converter canset the frequency setting interval of its output signal to FD.

[0035] Preferably, in the digital up-converter of the seventh, eighth,or ninth aspect, the first frequency converter may stop its frequencyconversion.

[0036] In the case where a multiple of the frequency setting intervalFD2 of the second frequency converter is equal to that of the frequencysetting interval FD of the output signal, the digital up-converter withthe above-described configuration can set the frequency setting intervalof its output signal to FD by means of only the second frequencyconverter.

[0037] In accordance with a tenth aspect of the present invention, thereis provided a receiver comprising a first frequency converter includinga first local oscillator and serving to frequency-convert a receivedsignal, the first local oscillator including the NCO of the first aspectoperating at the sampling frequency Fs and a phase locked loop (PLL)circuit having a multiplication ratio P (P is an integer) and acting toreceive the output signal from the NCO of the first aspect as areference signal, a second frequency converter including the NCO of thefirst aspect as a second local oscillator and serving to secondarilyfrequency-convert an output signal from the first frequency converter,and a demodulator for demodulating an output signal from the secondfrequency converter to extract received data therefrom, the receiverconverting the received signal into a baseband received signal with afrequency lower than that of the received signal by two frequencyconversions and extracting the received data from the converted basebandreceived signal, wherein: if a desired frequency setting interval of thereceived signal is FD and K1, K2 and L1 are arbitrary integers, thefirst frequency converter is adapted to frequency-convert the receivedsignal using a first specific signal output from the first localoscillator and set to a frequency setting interval of an FDP step, whereFDP=FD/K1×L1, the first local oscillator outputting the first specificsignal by accumulating the phase difference data by a modulo operationtaking a nearest integer of M1 as a modulus, where M1=Fs/FD×K1/L1×P; andthe second frequency converter is adapted to, if a sampling frequency ofthe output signal from the first frequency converter is Fs1,frequency-convert the output signal from the first frequency converterusing a second specific signal output from the second local oscillatorand set to a frequency setting interval of an FD2 step, where FD2=(FDmod FDP)/K2, the second local oscillator outputting the second specificsignal by accumulating the phase difference data by a modulo operationtaking a nearest integer of M2 as a modulus, where M2=Fs1/(FD modFDP)×K2.

[0038] The receiver with the above-described configuration converts thereceived signal into a baseband received signal with a frequency lowerthan that of the received signal by two frequency conversions. If thedesired frequency setting interval of the received signal is FD, K1, K2and L1 are arbitrary integers and the frequency setting interval FD isabove the frequency setting interval FDP of the first frequencyconverter and is indivisible by it, the deviation of the frequencydesired by the demodulator will exceed an allowable range. For thisreason, first, the first frequency converter frequency-converts thereceived signal using a frequency signal output from the first localoscillator including the PLL circuit with the multiplication ratio P andthe NCO of the first aspect and set to the frequency setting interval ofthe FD1 step, where FD1=FDP/P=FD/K1×L1/P. Then, the second frequencyconverter secondarily frequency-converts the output signal from thefirst frequency converter using a frequency signal output from the NCOof the first aspect as the second local oscillator and set to thefrequency setting interval of the FD2 step, where FD2=(FD mod FDP)/K2.Therefore, the receiver can accurately convert the frequency of thereceived signal input thereto at the frequency setting interval FD intothat desired by the demodulator.

[0039] In accordance with an eleventh aspect of the present invention,there is provided a receiver comprising a first frequency converterincluding a first local oscillator and serving to frequency-convert areceived signal, the first local oscillator including the NCO of thefirst aspect operating at the sampling frequency Fs and a PLL circuit(having a multiplication ratio P (P is an integer) and acting to receivethe output signal from the NCO of the first aspect as a referencesignal, a second frequency converter (for example, the frequencyconverter 12 of the sixth embodiment or the frequency converter 85 ofthe seventh embodiment) including the NCO of the first aspect as asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, and a demodulator fordemodulating an output signal from the second frequency converter toextract received data therefrom, the receiver converting the receivedsignal into a baseband received signal with a frequency lower than thatof the received signal by two frequency conversions and extracting thereceived data from the converted baseband received signal, wherein: if adesired frequency setting interval of the received signal is FD and K1,K2 and L1 are arbitrary integers, the first frequency converter isadapted to frequency-convert the received signal using a first specificsignal output from the first local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K1×L1, the first localoscillator outputting the first specific signal by accumulating thephase difference data by a modulo operation taking a nearest integer ofM1 as a modulus, where M1=Fs/FD×K1/L1×P; and the second frequencyconverter is adapted to, if a sampling frequency of the output signalfrom the first frequency converter is Fs1, frequency-convert the outputsignal from the first frequency converter using a second specific signaloutput from the second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=(FDP mod FD)/K2, the second localoscillator outputting the second specific signal by accumulating thephase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs1/(FDP mod FD)×K2.

[0040] The receiver with the above-described configuration converts thereceived signal into a baseband received signal with a frequency lowerthan that of the received signal by two frequency conversions. If thedesired frequency setting interval of the received signal is FD, K1, K2,and L1 are arbitrary integers and the frequency setting interval FD isbelow the frequency setting interval FDP of the first frequencyconverter and FDP is indivisible by FD, the deviation of the frequencydesired by the demodulator will exceed an allowable range. For thisreason, first, the first frequency converter frequency-converts thereceived signal using a frequency signal output from the first localoscillator including the PLL circuit with the multiplication ratio P andthe NCO of the first aspect and set to the frequency setting interval ofthe FD1 step, where FD1=FDP/P=FD/K1×L1/P. Then, the second frequencyconverter secondarily frequency-converts the output signal from thefirst frequency converter using a frequency signal output from the NCOof the first aspect as the second local oscillator and set to thefrequency setting interval of the FD2 step, where FD2=(FDP mod FD)/K2.Therefore, the receiver can accurately convert the frequency of thereceived signal input thereto at the frequency setting interval FD intothat desired by the demodulator.

[0041] In accordance with a twelfth aspect of the present invention,there is provided a receiver comprising a first frequency converterincluding a first local oscillator and serving to frequency-convert areceived signal, the first local oscillator including the NCO of thefirst aspect operating at the sampling frequency Fs and a PLL circuit(having a multiplication ratio P (P is an integer) and acting to receivethe output signal from the NCO of the first aspect as a referencesignal, a second frequency converter including the NCO of the firstaspect as a second local oscillator and serving to secondarilyfrequency-convert an output signal from the first frequency converter,and a demodulator for demodulating an output signal from the secondfrequency converter to extract received data therefrom, the receiverconverting the received signal into a baseband received signal with afrequency lower than that of the received signal by two frequencyconversions and extracting the received data from the converted basebandreceived signal, wherein: if a desired frequency setting interval of thereceived signal is FD and K1, K2 and L1 are arbitrary integers, thefirst frequency converter is adapted to frequency-convert the receivedsignal using a first specific signal output from the first localoscillator and set to a frequency setting interval of an FDP step, whereFDP=FD/K1×L1, the first local oscillator outputting the first specificsignal by accumulating the phase difference data by a modulo operationtaking a nearest integer of M1 as a modulus, where M1=Fs/FD×K1/L1×P; andthe second frequency converter is adapted to, if a sampling frequency ofthe output signal from the first frequency converter is Fs1,frequency-convert the output signal from the first frequency converterusing a second specific signal output from the second local oscillatorand set to a frequency setting interval of an FD2 step, where FD2=FD/K2,the second local oscillator outputting the second specific signal byaccumulating the phase difference data by a modulo operation taking anearest integer of M2 as a modulus, where M2=Fs1/FD×K2.

[0042] The receiver with the above-described configuration converts thereceived signal into a baseband received signal with a frequency lowerthan that of the received signal by two frequency conversions. If thedesired frequency setting interval of the received signal is FD, K1, K2and L1 are arbitrary integers, and the frequency setting interval FD ishigher than or equal to the frequency setting interval FDP of the firstfrequency converter and is evenly divisible by it, or FD is lower thanFDP and FDP is evenly divisible by FD, first, the first frequencyconverter frequency-converts the received signal using a frequencysignal output from the first local oscillator including the PLL circuitwith the multiplication ratio P and the NCO of the first aspect and setto the frequency setting interval of the FD1 step, whereFD1=FDP/P=FD/K1×L1/P. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the NCO of the first aspect as thesecond local oscillator and set to the frequency setting interval of theFD2 step, where FD2=FD/K2. Therefore, the receiver can accuratelyconvert the frequency of the received signal input thereto at thefrequency setting interval FD into that desired by the demodulator.

[0043] Preferably, in the receiver of the tenth, eleventh, or twelfthaspect, the second frequency converter may stop its frequencyconversion.

[0044] In the case where a multiple of the frequency setting intervalFD1 of the first frequency converter is equal to that of the frequencysetting interval FD of the received signal, the receiver with theabove-described configuration can accurately convert the frequency ofthe received signal input thereto at the frequency setting interval FDinto that desired by the demodulator by means of only the firstfrequency converter.

[0045] In accordance with a thirteenth aspect of the present invention,there is provided a transmitter comprising a modulator for modulatingand outputting a baseband transmit signal based on transmit data, afirst frequency converter including the NCO of the first aspect as afirst local oscillator and serving to frequency-convert the outputsignal from the modulator, a second frequency converter including asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, the second localoscillator including the NCO of the first aspect operating at thesampling frequency Fs and a PLL circuit having a multiplication ratio P(P is an integer) and acting to receive the output signal from the NCOof the first aspect as a reference signal, the transmitter convertingand outputting the baseband transmit signal into a transmit signal witha frequency higher than that of the baseband transmit signal by twofrequency conversions, wherein: if a desired frequency setting intervalof the transmit signal is FD and K1, K2 and L2 are arbitrary integers,the second frequency converter is adapted to frequency-convert theoutput signal from the first frequency converter using a first specificsignal output from the second local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K2×L2, the second localoscillator outputting the first specific signal by accumulating thephase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs/FD×K2/L2×P; and the first frequencyconverter is adapted to, if a sampling frequency of the output signalfrom the modulator is Fs1, frequency-convert the output signal from themodulator using a second specific signal output from the first localoscillator and set to a frequency setting interval of an FD1 step, whereFD1=(FD mod FDP)/K1, the first local oscillator outputting the secondspecific signal by accumulating the phase difference data by a modulooperation taking a nearest integer of M1 as a modulus, where M1=Fs1/(FDmod FDP)×K1.

[0046] The transmitter with the above-described configuration convertsand outputs the baseband transmit signal into a transmit signal with afrequency higher than that of the baseband transmit signal by twofrequency conversions.

[0047] If the desired frequency setting interval of the transmit signalis FD, K1, K2 and L2 are arbitrary integers and the frequency settinginterval FD is above the frequency setting interval FDP of the secondfrequency converter and is indivisible by it, the frequency deviation ofthe transmit signal from the transmitter will exceed an allowable range.For this reason, first, the first frequency converter frequency-convertsthe baseband transmit signal using a frequency signal output from theNCO of the first aspect as the first local oscillator and set to thefrequency setting interval of the FD1 step, where FD1=(FD mod FDP)/K1.Then, the second frequency converter secondarily frequency-converts theoutput signal from the first frequency converter using a frequencysignal output from the second local oscillator including the PLL circuitwith the multiplication ratio P and the NCO of the first aspect and setto the frequency setting interval of the FD2 step, whereFD2=FDP/P=FD/K2×L2/P. Therefore, the transmitter can accurately convertthe frequency of the baseband transmit signal from the modulator into atarget transmit signal frequency.

[0048] In accordance with a fourteenth aspect of the present invention,there is provided a transmitter comprising a modulator for modulatingand outputting a baseband transmit signal based on transmit data, afirst frequency converter including the NCO of the first aspect as afirst local oscillator and serving to frequency-convert the outputsignal from the modulator, a second frequency converter including asecond local oscillator and serving to secondarily frequency-convert anoutput signal from the first frequency converter, the second localoscillator including the NCO of the first aspect operating at thesampling frequency Fs and a PLL circuit having a multiplication ratio P(P is an integer) and acting to receive the output signal from the NCOof the first aspect as a reference signal, the transmitter convertingand outputting the baseband transmit signal into a transmit signal witha frequency higher than that of the baseband transmit signal by twofrequency conversions, wherein: if a desired frequency setting intervalof the transmit signal is FD and K1, K2 and L2 are arbitrary integers,the second frequency converter is adapted to frequency-convert theoutput signal from the first frequency converter using a first specificsignal output from the second local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K2×L2, the second localoscillator outputting the first specific signal by accumulating thephase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs/FD×K2/L2×P; and the first frequencyconverter is adapted to, if a sampling frequency of the output signalfrom the modulator is Fs1, frequency-convert the output signal from themodulator using a second specific signal output from the first localoscillator and set to a frequency setting interval of an FD1 step, whereFD1=(FDP mod FD)/K1, the first local oscillator outputting the secondspecific signal by accumulating the phase difference data by a modulooperation taking a nearest integer of M1 as a modulus, where M1=Fs1/(FDPmod FD)×K1.

[0049] The transmitter with the above-described configuration convertsand outputs the baseband transmit signal into a transmit signal with afrequency higher than that of the baseband transmit signal by twofrequency conversions.

[0050] If the desired frequency setting interval of the transmit signalis FD, K1, K2, and L2 are arbitrary integers and the frequency settinginterval FD is below the frequency setting interval FD2 of the secondfrequency converter and FD2 is indivisible by FD, the frequencydeviation of the transmit signal from the transmitter will exceed anallowable range. For this reason, first, the first frequency converterfrequency-converts the baseband transmit signal using a frequency signaloutput from the NCO of the first aspect as the first local oscillatorand set to the frequency setting interval of the FD1 step, whereFD1=(FDP mod FD)/K1. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the second local oscillatorincluding the PLL circuit with the multiplication ratio P and the NCO ofthe first aspect and set to the frequency setting interval of the FD2step, where FD2=FDP/P=FD/K2×L2/P. Therefore, the transmitter canaccurately convert the frequency of the baseband transmit signal fromthe modulator into a target transmit signal frequency.

[0051] In accordance with a fifteenth aspect of the present invention,there is provided a transmitter comprising a modulator for modulatingand outputting a baseband transmit signal based on transmit data, afirst frequency converter including the NCO of the first aspect as afirst local and serving to frequency-convert the output signal from themodulator, a second frequency converter including a second localoscillator and serving to secondarily frequency-convert an output signalfrom the first frequency converter, the second local oscillatorincluding the NCO of the first aspect operating at the samplingfrequency Fs and a PLL circuit having a multiplication ratio P (P is aninteger) and acting to receive the output signal from the NCO of thefirst aspect as a reference signal, the transmitter converting andoutputting the baseband transmit signal into a transmit signal with afrequency higher than that of the baseband transmit signal by twofrequency conversions, wherein: if a desired frequency setting intervalof the transmit signal is FD and K1, K2 and L2 are arbitrary integers,the second frequency converter is adapted to frequency-convert theoutput signal from the first frequency converter using a first specificsignal output from the second local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K2×L2, the second localoscillator outputting the first specific signal by accumulating thephase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs/FD×K2/L2×P; and the first frequencyconverter is adapted to, if a sampling frequency of the output signalfrom the modulator is Fs1, frequency-convert the output signal from themodulator using a second specific signal output from the first localoscillator and set to a frequency setting interval of an FD1 step, whereFD1=FD/K1, the first local oscillator outputting the second specificsignal by accumulating the phase difference data by a modulo operationtaking a nearest integer of M1 as a modulus, where M1=Fs1/FD×K1.

[0052] The transmitter with the above-described configuration convertsand outputs the baseband transmit signal into a transmit signal with afrequency higher than that of the baseband transmit signal by twofrequency conversions.

[0053] If the desired frequency setting interval of the transmit signalis FD, K1, K2, and L2 are arbitrary integers, and the frequency settinginterval FD is higher than or equal to the frequency setting intervalFD2 of the second frequency converter and is evenly divisible by it, orFD is lower than FD2 and FD2 is evenly divisible by FD, the frequencydeviation of the transmit signal from the transmitter will exceed anallowable range. For this reason, first, the first frequency converterfrequency-converts the baseband transmit signal using a frequency signaloutput from the NCO of the first aspect as the first local oscillatorand set to the frequency setting interval of the FD1 step, whereFD1=FD/K1. Then, the second frequency converter secondarilyfrequency-converts the output signal from the first frequency converterusing a frequency signal output from the second local oscillatorincluding the PLL circuit with the multiplication ratio P and the NCO ofthe first aspect and set to the frequency setting interval of the FD2step, where FD2=FDP/P=FD/K2×L2/P. Therefore, the transmitter canaccurately convert the frequency of the baseband transmit signal fromthe modulator into a target transmit signal frequency.

[0054] Preferably, in the transmitter of the thirteenth, fourteenth, orfifteenth aspect, the first frequency converter may stop its frequencyconversion.

[0055] In the case where a multiple of the frequency setting intervalFD2 of the second frequency converter is equal to that of the frequencysetting interval FD of the transmit signal, the transmitter with theabove-described configuration can accurately convert the frequency ofthe baseband transmit signal from the modulator into that of a targettransmit signal by means of only the second frequency converter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The above and other objects, features, and advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0057]FIG. 1 is a block diagram illustrating the configuration of anumerical control oscillator according to a first embodiment of thepresent invention;

[0058]FIG. 2 is a graph illustrating a comparison of simulation resultsof spurious characteristics between a conventional numerical controloscillator and the numerical control oscillator of the first embodiment;

[0059]FIG. 3 is a block diagram illustrating the configuration of anembodiment of a digital down-converter using the numerical controloscillator of the first embodiment;

[0060]FIG. 4 is a block diagram illustrating the configuration of anembodiment of a digital up-converter using the numerical controloscillator of the first embodiment;

[0061]FIG. 5 is a block diagram illustrating the configuration of analternative embodiment of the digital down-converter using the numericalcontrol oscillator of the first embodiment;

[0062]FIG. 6 is a block diagram illustrating the configuration of analternative embodiment of the digital up-converter using the numericalcontrol oscillator of the first embodiment;

[0063]FIG. 7 is a block diagram illustrating the configuration of anembodiment of a receiver using the numerical control oscillator of thefirst embodiment;

[0064]FIG. 8 is a block diagram illustrating the configuration of analternative embodiment of the receiver using the numerical controloscillator of the first embodiment; and

[0065]FIG. 9 is a block diagram illustrating the configuration of atransmitter using the numerical control oscillator of the firstembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Preferred embodiments of the present invention will be describedin detail herein below with reference to the annexed drawings. In thefollowing description, a detailed description of known functions andconfigurations incorporated herein will be omitted when it may make thesubject matter of the present invention rather unclear.

[0067]FIG. 1 is a block diagram illustrating the configuration of anumerical control oscillator (NCO) of the first embodiment. Asillustrated in FIG. 1, the NCO comprises a phase accumulator 1 foraccumulating input phase difference data to generate phase data, and amemory, preferably a read only memory (ROM), 2 for storing aphase/amplitude conversion table to output amplitude data correspondingto the phase data generated by the phase accumulator 1.

[0068] In detail, on the assumption that a sampling frequency of anoutput signal from the NCO is Fs, the upper limit of a desired frequencysetting interval of the output signal is FD, and K and L are arbitraryintegers, the phase accumulator 1 includes a phase register 1 a forstoring and outputting the phase data, and a phase calculator 1 b foradding or subtracting the input phase difference data and the phase datafrom the phase register 1 a to or from each other by a modulo operationtaking the nearest integer of M as a modulus, where M=Fs/FD×K/L.Therefore, the phase accumulator 1 accumulates the phase difference dataas an input signal to the NCO to generate the phase data.

[0069] The ROM 2 has its address terminal connected to an outputterminal of the phase accumulator 1 by j-bit wiring, where j=log₂M(where, j is rounded up to the nearest integer), and stores thephase/amplitude conversion table, which includes M amplitude data.Therefore, the ROM 2 outputs the amplitude data corresponding to thephase data, input from the phase accumulator 1 to the address terminal,through its data terminal as the output signal of the NCO. As a result,the NCO of the present embodiment provides its output signal set to afrequency setting interval of a dF step, where dF=FD/K×L.

[0070] For example, assuming that the sampling frequency Fs of theoutput signal from the NCO is 153.6 MHz, the upper limit FD of thedesired frequency setting interval of the output signal is 200 KHz, andK and L are 1 s, the phase calculator 1 b adds or subtracts the inputphase difference data and the phase data from the phase register 1 a toor from each other by a modulo operation taking M=“768” as a modulus,where M=Fs/FD×K/L=153.6[MHz]/200[KHz]=768.

[0071] Also, the address terminal of the ROM 2 is connected to theoutput terminal of the phase accumulator 1 by the j-bit wiring, wherej=log₂M=log₂768≈9.58=10 (where, j is rounded up to the nearest integer),namely, 10-bit wiring.

[0072] Therefore, the word length of the ROM 2 and the phase word lengthof the phase calculator 1 b become equal, and as a result there is noneed to requantize an address word length (the word length of the ROM 2)from the phase calculator 1 b. Therefore, it is possible to realize alow-spurious NCO which has no error e^(p) resulting from requantizationand provides its output signal based on only low-capacity amplitude dataof 768 words necessary for the modulo operation based on the modulus of“768” under the condition that the sampling frequency Fs of the outputsignal is 153.6 MHz and the frequency setting interval dF is FD/K×L=200KHz.

[0073] Further, the NCO with the above-described configuration can havesettings corresponding to respective communication systems (for example,a W-CDMA mobile phone system, an IS-95 mobile phone system and an IEEE802.11a wireless LAN system), including the above-described exemplaryvalues, as shown in the below table 1. TABLE 1 No. FD[KHz] Fs[MHz]dF[KHz] K L M W-CDMA 1 200 61.44 40 5 1 1536 2 200 61.44 80 5 2 768 3200 92.16 40 5 1 2304 4 200 122.88 40 5 1 3072 5 200 153.6 200 1 1 768 6200 153.6 1600 1 8 96 7 200 184.32 200 5 1 4608 IS-95 Band Class 0 8 3098.304 6 5 1 16384 9 30 98.304 12 5 2 8192 IEEE 802.11a 10 20000 10020000 1 1 5 11 20000 200 20000 1 1 10

[0074] As one example of the above table 1, assuming that the samplingfrequency Fs of the output signal from the NCO is 61.44 MHz, the upperlimit FD of the desired frequency setting interval of the output signalis 200 KHz, K is 5, and L is 1, the output signal is provided based ononly low-capacity amplitude data of 1536 words necessary for a modulooperation taking M=“1536” as a modulus by the phase calculator 1 b,where M=Fs/FD×K/L=61.44[MHz]/200[KHz]×5=1536. That is, it is possible torealize a low-spurious NCO which provides its output signal based ononly low-capacity amplitude data under the condition that the samplingfrequency Fs of the output signal is 61.44 MHz and the frequency settinginterval dF is FD/K×L=200[KHz]/5=40[KHz].

[0075]FIG. 2 is a graph illustrating a comparison of simulation resultsof spurious characteristics between a conventional NCO that performs amodulo operation taking 2^(j) as a modulus (a parameter is representedby a phase word length j and the number of amplitude data in thephase/amplitude conversion table) and the NCO of the first embodiment (aparameter is represented by only the number of amplitude data in thephase/amplitude conversion table) under the above-described condition,wherein the axis of abscissa represents an amplitude data bit lengthoutput from the ROM 2, the axis of ordinate represents a spurious, andthe number of amplitude data in the phase/amplitude conversion tablestored in the ROM 2 represents a parameter. As illustrated in FIG. 2, inthe case where the NCO of the present embodiment makes the word lengthof the ROM 2 shorter to use amplitude data of, for example, 384 words,192 words or 96 words, the spurious characteristics thereof are severelyworsened. However, as long as the NCO generates phase data by adding orsubtracting the input phase difference data and the phase data from thephase register 1 a to or from each other by a modulo operation takingthe nearest integer of M as a modulus, where M=Fs/FD×K/L, namely, M=768under the above condition, it can obtain the same spuriouscharacteristics as those of a conventional NCO that performs a modulooperation taking 2²⁰ as a modulus and requires amplitude data of about1M words.

[0076] Next, a description will be given of examples of applications ofthe NCO of the first embodiment with reference to the accompanyingdrawings. For example, the NCO of the first embodiment may be used in adigital down-converter as shown in FIG. 3.

[0077]FIG. 3 is a block diagram illustrating the configuration of anembodiment of a digital down-converter 11 using the NCO of the firstembodiment. As illustrated in FIG. 3, the digital down-converter 11comprises a frequency converter 12 for frequency-converting an inputsignal of a center frequency Fif1 to obtain a complex signal (zero IFsignal) of a center frequency Fif2=0[Hz]. The frequency converter 12includes a local oscillator 12 a using the NCO of the first embodiment,for generating a complex local signal of a frequency Fc (containing areal component “C(t)=cos(2π×Fc×t)” and an imaginary component“−S(t)=−sin(2π×Fc×t)” whose phase is 90 degrees ahead of that of thereal component), and multipliers 12 b and 12 c for multiplying the inputsignal by the real and imaginary components of the complex local signalgenerated by the local oscillator 12 a, respectively.

[0078] A decimator 13 decimates the complex signal from the frequencyconverter 12. To this end, the decimator 13 includes real and imaginarydecimators 13 a and 13 b each for multiplying a sampling frequency Fs1of a corresponding one of real and imaginary components of the complexsignal by 1/N to convert it into a sampling frequency Fs2=Fs1/N. Aroll-off filter 14 band-limits the complex signal decimated by thedecimator 13 to a target signal band to output the resulting complexsignal (I,Q). To this end, the roll-off filter 14 includes a real filter14 a and an imaginary filter 14 b.

[0079] For example, assuming that a desired frequency setting intervalFD of an input signal is evenly divisible by a frequency settinginterval dF of the frequency converter 12, the digital down-converter 11is operated in the following marmer. In this case, if K and L arearbitrary integers, the frequency converter 12 sets phase differencedata φ to the local oscillator 12 a using the NCO of the firstembodiment to a value of φ=Fc/dF=Fc/FD×K/L. Then, the frequencyconverter 12 accurately converts an input signal of a center frequencyFif1 into a complex signal of a center frequency Fif2 using a complexlocal signal of a frequency Fc output from the local oscillator 12 a andset to a frequency setting interval of a dF step, where dF=FD/K×L. Here,the local oscillator 12 a outputs the complex local signal of thefrequency Fc by accumulating the phase difference data by a modulooperation taking the nearest integer of M as a modulus, whereM=Fs1/FD×K/L.

[0080] More specifically, assuming that a sampling frequency Fs1 of aninput signal is 153.6 MHz, a desired frequency setting interval FD ofthe input signal is 200 KHz, a center frequency Fif1 of the input signalis 36.4 MHz and K=L=1, the frequency converter 12 sets phase differencedata φ to the local oscillator 12 a using the NCO of the firstembodiment to φ=Fc/dF=Fc/FD×K/L=36.4[MHz]/200[KHz]=182. Then, thefrequency converter 12 accurately converts the input signal of thecenter frequency Fif1 into a complex signal (zero IF signal) of a centerfrequency Fif2=0[Hz] using a complex local signal of a frequencyFc=36.4[MHz] output from the local oscillator 12 a and set to afrequency setting interval of a dF step, where dF=FD/K×L=200[KHz]. Here,the local oscillator 12 a outputs the complex local signal of thefrequency Fc by accumulating the phase difference data by a modulooperation taking M=768 as a modulus, whereM=Fs1/FD×K/L=153.6[MHz]/200[KHz]=768.

[0081] The NCO of the first embodiment may also be used in a digitalup-converter as illustrated in FIG. 4.

[0082]FIG. 4 is a block diagram illustrating the configuration of anembodiment of a digital up-converter using the NCO of the firstembodiment. As illustrated in FIG. 4, the digital up-converter comprisesa roll-off filter 21 for band-limiting an input complex signal(containing baseband signal components I and Q) of a center frequencyFif1=0[Hz] to a target signal band. The roll-off filter 21 includes areal filter 21 a and an imaginary filter 21 b. An interpolator 22interpolates the complex signal band-limited by the roll-off filter 21.To this end, the interpolator 22 includes real and imaginaryinterpolators 22 a and 22 b each for multiplying a sampling frequencyFs1 of a corresponding one of real and imaginary components of thecomplex signal by N to convert it into a sampling frequency Fs2=Fs1×N.

[0083] A frequency converter 23 frequency-converts an output signal fromthe interpolator 22 to output a real signal of a target center frequencyFif2. To this end, the frequency converter 23 includes a localoscillator 23 a using the NCO of the first embodiment, for generating acomplex local signal of a frequency Fc (containing a real component“C(t)=cos(2π×Fc×t)” and an imaginary component “S(t)=sin(2π×Fc×t)” whosephase is 90 degrees delayed from that of the real component),multipliers 23 b and 23 c for multiplying real and imaginary componentsof the output signal from the interpolator 22 by the real and imaginarycomponents of the complex local signal generated by the local oscillator23 a, respectively, and a subtracter 23 d for subtracting output signalsfrom the multipliers 23 b and 23 c from each other.

[0084] For example, assuming that a desired frequency setting intervalFD of an output signal is evenly divisible by a frequency settinginterval dF of the frequency converter 23, the digital up-converter isoperated in the following manner. In this case, if K and L are arbitraryintegers, the frequency converter 23 sets phase difference data φ to thelocal oscillator 23 a using the NCO of the first embodiment to a valueof φ=Fc/dF=Fc/FD×K/L. Then, the frequency converter 23 accuratelyconverts a baseband signal of a center frequency Fif1 into a complexsignal of a target center frequency Fif2 using a complex local signal ofa frequency Fc output from the local oscillator 23 a and set to afrequency setting interval of a dF step, where dF=FD/K×L. Here, thelocal oscillator 23 a outputs the complex local signal of the frequencyFc by accumulating the phase difference data by a modulo operationtaking the nearest integer of M as a modulus, where M=Fs2/FD×K/L.

[0085] In detail, assuming that a sampling frequency Fs2 of an outputsignal is 153.6 MHz, a desired frequency setting interval FD of theoutput signal is 200 KHz, a center frequency Fif2 of the output signalis 72.8 MHz and K=L=1, the frequency converter 23 sets phase differencedata φ to the local oscillator 23 a using the NCO of the firstembodiment to φ=Fc/dF=Fc/FD×K/L=72.8[MHz]/200[KHz]=364. Then, thefrequency converter 23 accurately converts a baseband signal of a centerfrequency Fif1=0[Hz] into a complex signal of a target center frequencyFif2 using a complex local signal of a frequency Fc=72.8[MHz] outputfrom the local oscillator 23 a and set to a frequency setting intervalof a dF step, where dF=FD/K×L=200[KHz]. Here, the local oscillator 23 aoutputs the complex local signal of the frequency Fc by accumulating thephase difference data by a modulo operation taking M=768 as a modulus,where M=Fs2/FD×K/L=153.6[MHz]/200[KHz]=768.

[0086] Next, a description will be given of the configuration of analternative embodiment of the digital down-converter using the NCO ofthe first embodiment, which comprises first and second frequencyconverters each including the NCO as a local oscillator and serves toconvert and output an input signal into a signal with a frequency lowerthan that of the input signal by two frequency conversions.

[0087]FIG. 5 is a block diagram illustrating the configuration of thealternative embodiment of the digital down-converter using the numericalcontrol oscillator of the first embodiment. As illustrated in FIG. 5,the digital down-converter comprises a frequency converter 31 forfrequency-converting an input signal of a center frequency Fif1 toobtain a complex signal of a center frequency Fif2. The frequencyconverter 31 includes a local oscillator 31 a using the NCO of the firstembodiment, for generating a complex local signal of a frequency Fc1(containing a real component “C1(t)=cos(2π×Fc1×t)” and an imaginarycomponent “−S1(t)=−sin(2π×Fc1×t)” whose phase is 90 degrees ahead ofthat of the real component), and multipliers 31 b and 31 c formultiplying the input signal by the real and imaginary components of thecomplex local signal generated by the local oscillator 31 a,respectively.

[0088] A decimator 32 decimates the complex signal from the frequencyconverter 31. To this end, the decimator 32 includes real and imaginarydecimators 32 a and 32 b each for multiplying a sampling frequency Fs1of a corresponding one of real and imaginary components of the complexsignal by 1/N to convert it into a sampling frequency Fs2=Fs1/N. Afrequency converter 33 frequency-converts the complex signal decimatedby the decimator 32 to obtain a complex signal of a center frequencyFif3. The frequency converter 33 includes a local oscillator 33 a usingthe NCO of the first embodiment, for generating a complex local signalof a frequency Fc2 (containing a real component “C2(t)=cos(2π×Fc2×t)”and an imaginary component “−S2(t)=−sin(2π×Fc2×t)” whose phase is 90degrees ahead of that of the real component), and multipliers 33 b, 33c, 33 d, and 33 e, a subtracter 33 f and an adder 33 g for performingmultiplication, subtraction and addition operations with respect to thecomplex signal decimated by the decimator 32 and the complex localsignal generated by the local oscillator 33 a, respectively.

[0089] A roll-off filter 34 band-limits the complex signal from thefrequency converter 33 to a target signal band to output the resultingcomplex signal (I,Q) of the center frequency Fif3. The roll-off filter34 includes a real filter 34 a and an imaginary filter 34 b.

[0090] For example, assuming that a sampling frequency of an inputsignal is Fs1, and a desired frequency setting interval FD of the inputsignal is above a frequency setting interval FD1 of the frequencyconverter 31 and is indivisible by it, the digital down-converter isoperated in the following manner. In this case, if K1, K2, and L1 arearbitrary integers, the frequency converter 31 sets phase differencedata φ1 to the local oscillator 31 a using the NCO of the firstembodiment to a value of φ1=Fc1/FD1=Fc1/FD×K1/L1. Then, the frequencyconverter 31 converts an input signal of a center frequency Fif1 into acomplex signal of a center frequency Fif2 using a complex local signalof a frequency Fc1 output from the local oscillator 31 a and set to afrequency setting interval of an FD1 step, where FD1=FD/K1×L1. Here, thelocal oscillator 31 a outputs the complex local signal of the frequencyFc1 by accumulating the phase difference data by a modulo operationtaking the nearest integer of M1 as a modulus, where M1=Fs1/FD×K1/L1.

[0091] Also, the frequency converter 33 sets phase difference data φ2 tothe local oscillator 33 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/(FD mod FD1)×K2. Then, the frequency converter33 converts the complex signal of the center frequency Fif2 into acomplex signal of a center frequency Fif3 using a complex local signalof a frequency Fc2 output from the local oscillator 33 a and set to afrequency setting interval of an FD2 step, where FD2=(FD mod FD1)/K2.Here, the local oscillator 33 a outputs the complex local signal of thefrequency Fc2 by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs2/(FD mod FD1)×K2.

[0092] More specifically, assuming that a sampling frequency Fs1 of aninput signal is 98.304 MHz, a desired frequency setting interval FD ofthe input signal is 30 KHz, a center frequency Fif1 of the input signalis 13.742 MHz, K1=15 and L1=8, the frequency converter 31 sets phasedifference data φ1 to the local oscillator 31 a using the NCO of thefirst embodiment toφ1=Fc1/FD1=Fc1/FD×K1/L1=13.728[MHz]/30[KHz]×15/8=858. The frequencyconverter 31 accurately converts the input signal of the centerfrequency Fif1 into a complex signal of a center frequency Fif2 =14[Hz]using a complex local signal of a frequency Fc1=13.728[MHz] output fromthe local oscillator 31 a and set to a frequency setting interval of anFD1 step, where FD1=FD/K1×L1=30[KHz]/15×8=16[KHz]. Here, the localoscillator 31 a outputs the complex local signal of the frequency Fc1 byaccumulating the phase difference data by a modulo operation takingM1=6144 as a modulus, whereM1=Fs1/FD×K/L1=98.304[MHz]/30[KHz]×15/8=6144.

[0093] Also, assuming that a decimation rate N of the decimator 32 is 10and K2=7, the frequency converter 33 sets phase difference data φ2 tothe local oscillator 33 a using the NCO of the first embodiment toφ2=Fc2/FD2=Fc2/(FD mod FD1)×K2=14[KHz]/(30[KHz] mod 16[KHz])×7=7. Then,the frequency converter 33 accurately converts the complex signal of thecenter frequency Fif2 into a complex signal (zero IF signal) of a centerfrequency Fif3=0[Hz] using a complex local signal of a frequency Fc2output from the local oscillator 33 a and set to a frequency settinginterval of an FD2 step, where FD2=(FD mod FD1)/K2=(30[KHz] mod16[KHz])/7=2[KHz]. Here, the local oscillator 33 a outputs the complexlocal signal of the frequency Fc2 by accumulating the phase differencedata by a modulo operation taking the nearest integer of M2, 4915, as amodulus, where M2=Fs2/(FD mod FD1)×K2=9.8304[MHz]/(30[KHz] mod16[KHz])×7.

[0094] However, for example, assuming that a desired frequency settinginterval FD of an input signal is below a frequency setting interval FD1of the frequency converter 31 and FD1 is indivisible by FD, thefrequency converter 31 sets phase difference data φ1 to the localoscillator 31 a using the NCO of the first embodiment to a value ofφ1=Fc1/FD1=Fc1/FD×K1/L1. Then, the frequency converter 31 converts aninput signal of a center frequency Fif1 into a complex signal of acenter frequency Fif2 using a complex local signal of a frequency Fc1output from the local oscillator 31 a and set to a frequency settinginterval of an FD1 step, where FD1=FD/K1×L1. Here, the local oscillator31 a outputs the complex local signal of the frequency Fc1 byaccumulating the phase difference data by a modulo operation taking thenearest integer of M1 as a modulus, where M1=Fs1/FD×K1/L1.

[0095] Also, the frequency converter 33 sets phase difference data φ2 tothe local oscillator 33 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/(FD1 mod FD)×K2. Then, the frequency converter33 converts the complex signal of the center frequency Fif2 into acomplex signal of a center frequency Fif3 using a complex local signalof a frequency Fc2 output from the local oscillator 33 a and set to afrequency setting interval of an FD2 step, where FD2=(FD1 mod FD)/K2.Here, the local oscillator 33 a outputs the complex local signal of thefrequency Fc2 by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs2/(FD1 mod FD)×K2.

[0096] Conversely, for example, assuming that a desired frequencysetting interval FD of an input signal is higher than or equal to afrequency setting interval FD1 of the frequency converter 31 and isevenly divisible by it, or that FD is lower than FD1 and FD1 is evenlydivisible by FD, the frequency converter 31 sets phase difference dataφ1 to the local oscillator 31 a using the NCO of the first embodiment toa value of φ1=Fc1/FD1=Fc1/FD×K1/L1. Then, the frequency converter 31converts an input signal of a center frequency Fif1 into a complexsignal of a center frequency Fif2 using a complex local signal of afrequency Fc1 output from the local oscillator 31 a and set to afrequency setting interval of an FD1 step, where FD1=FD/K1×L1. Here, thelocal oscillator 31 a outputs the complex local signal of the frequencyFc1 by accumulating the phase difference data by a modulo operationtaking the nearest integer of M1 as a modulus, where M1=Fs1/FD×K1/L1.

[0097] Also, the frequency converter 33 sets phase difference data φ2 tothe local oscillator 33 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/FD×K2. Then, the frequency converter 33 convertsthe complex signal of the center frequency Fif2 into a complex signal ofa center frequency Fif3 using a complex local signal of a frequency Fc2output from the local oscillator 33 a and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2. Here, the local oscillator 33a outputs the complex local signal of the frequency Fc2 by accumulatingthe phase difference data by a modulo operation taking the nearestinteger of M2 as a modulus, where M2=Fs2/FD×K2.

[0098] However, in the case where a multiple of the frequency settinginterval FD1 of the frequency converter 31 is equal to that of thefrequency setting interval FD of the input signal, the digitaldown-converter with the above-described configuration can convert thefrequency of the input signal input thereto at the frequency settinginterval FD into a desired frequency within the range of an allowablefrequency deviation by means of only the frequency converter 31. In thiscase, the frequency conversion by the frequency converter 33 may bestopped.

[0099] Further, the digital down-converter with the above-statedconfiguration can have various settings of the respective parameters,including the above-described exemplary values, as shown in the belowtables 2 to 5. The tables 2 and 3 show examples of settings of therespective parameters in a W-CDMA system, the table 4 shows examples ofsettings of the respective parameters in an IS-95 Band (Class 0) system,and the table 5 shows examples of settings of the respective parametersin an IEEE 802.11a system.

[0100] It should be noted that, in the tables, examples having nodescription of settings of the parameters associated with the frequencyconverter 33 are realizable by the digital down-converter configurationof FIG. 3 and those parameters are again readable as the correspondingparameters. TABLE 2 Fifa Fif1 FD FD1 Fs1 Fc1 No. [MHz] [MHz] [KHz] [KHz][MHz] [MHz] K1 L1 M1 ΔØ1 1 190.00 5.680 200.0 40.0 61.440 5.680 5 1 1536142 2 190.00 5.680 200.0 40.0 92.160 5.680 5 1 2304 142 3 190.00 −55.760200.0 40.0 122.880 −55.760 5 1 3072 −1394 4 189.60 36.000 200.0 200.0153.600 36.000 1 1 768 180 5 189.80 36.200 200.0 200.0 153.600 36.200 11 768 181 6 190.00 36.400 200.0 200.0 153.600 36.400 1 1 768 182 7190.15 36.550 200.0 200.0 153.600 36.400 1 1 768 182 8 190.20 36.600200.0 200.0 153.600 36.600 1 1 768 183 9 190.35 36.750 200.0 200.0153.600 36.600 1 1 768 183 10 190.40 36.800 200.0 200.0 153.600 36.800 11 768 184 11 189.80 36.200 200.0 1600.0 153.600 35.200 1 8 96 22 12190.00 36.400 200.0 1600.0 153.600 35.200 1 8 96 22 13 190.20 36.600200.0 1600.0 153.600 35.200 1 8 96 22 14 190.00 5.680 200.0 40.0 184.3205.680 5 1 4608 142

[0101] TABLE 3 Fif2 Fs2 FD2 Fc2 No. [KHz] [MHz] [KHz] [KHz] K2 M2 ΔØ2 1— — — — — — — 2 — — — — — — — 3 — — — — — — — 4 — — — — — — — 5 — — — —— — — 6 — — — — — — — 7 150.0 30.72 50.000 150.10 4 614 3 8 — — — — — —— 9 150.0 30.72 50.000 150.10 4 614 3 10 — — — — — — — 11 1000.0 30.7240.000 1000.00 5 768 25 12 1200.0 30.72 40.000 1200.00 5 768 30 131400.0 30.72 40.000 1400.00 5 768 35 14 — — — — — — —

[0102] TABLE 4 Fifa Fif1 FD FD1 Fs1 Fc1 No. [MHz] [MHz] [KHz] [KHz][MHz] [MHz] K1 L1 M1 ΔØ1 1 210.35 13.742 30.0 16.0 98.304 13.728 15 86144 858 2 210.38 13.772 30.0 16.0 98.304 13.760 15 8 6144 860 3 210.4113.802 30.0 16.0 98.304 13.792 15 8 6144 862 4 210.35 53.064 30.0 11.3157.286 53.055 8 3 13981 4716 5 210.38 53.094 30.0 11.3 157.286 53.089 83 13981 4719 6 210.41 53.124 30.0 11.3 157.286 53.123 8 3 13981 4722Fif2 Fs2 FD2 Fc2 No. [KHz] [MHz] [KHz] [KHz] K2 M2 ΔØ2 1 14.00 9.83042.000 14.00 7 4915 7 2 12.00 9.8304 2.000 12.00 7 4915 6 3 10.00 9.83042.000 10.00 7 4915 5 4 8.60 9.8304 1.250 8.75 6 7864 7 5 4.90 9.83041.250 5.00 6 7864 4 6 1.10 9.8304 1.250 1.25 6 7864 1

[0103] TABLE 5 Fifa Fif1 FD FD1 Fs1 Fc1 No. [MHz] [MHz] [KHz] [KHz][MHz] [MHz] K1 L1 M1 ΔØ1 1 180.00 −20.000 100.0 100.0 100.000 −20.000 11 1000 −200 2 179.80 −20.200 200.0 400.0 200.000 −20.400 1 2 500 −51 3180.00 −20.000 200.0 400.0 200.000 −20.000 1 2 500 −50 4 180.20 −19.800200.0 400.0 200.000 −20.000 1 2 500 −50 Fif2 Fs2 FD2 Fc2 No. [KHz] [MHz][KHz] [KHz] K2 M2 ΔØ2 1 — — — — — — — 2 200.0 20 200.000 200.00 1 100 13 — — — — — — — 4 200.0 20 200.000 200.00 1 100 1

[0104] In the digital-down converter of the present embodiment, wherethe frequency setting interval FD1 of the frequency converter 31 issettable at a step lower than or equal to the desired frequency settinginterval FD of the input signal, each frequency can be input by merelychanging the setting of frequency data (phase difference data) to theNCO of the frequency converter 31. Therefore, a data setting time of acontroller that controls the digital down-converter can be reduced byhalf compared with a conventional digital down-converter requiring thesetting of data to both frequency converters and the frequency data tothe NCO can be computed in a simpler manner.

[0105] More specifically, for example, where a frequency is set at a 200KHz step between a lower IF limit and an upper IF limit on theassumption that the lower IF limit is 180 MHz, the upper IF limit is 200MHz and the sampling frequency Fs1=153.6 MHz, the digital down-converterin which the frequency setting interval dF of the input signal is 200KHz can set the phase difference data φ to 132 for the lower IF limit,and to 232 for the upper IF limit by incrementing the phase differencedata φ by “1” whenever changing the IF by 200 KHz.

[0106] Additionally, the NCO of the first embodiment may be used in adigital up-converter as illustrated in FIG. 6. In the case where acenter frequency Fif3 of an output signal is indivisible by a desiredfrequency setting interval FD of the output signal, the digitalup-converter comprises a first frequency converter, and a secondfrequency converter including the NCO as a local oscillator, and servesto perform two frequency conversions to convert an input signal into asignal with a frequency higher than that of the input signal and outputthe converted signal as a signal sampled at a sampling frequency Fs.

[0107]FIG. 6 is a block diagram illustrating the configuration of analternative embodiment of the digital up-converter using the NCO of thefirst embodiment. As illustrated in FIG. 6, the digital up-convertercomprises a roll-off filter 41 for band-limiting an input complex signal(containing baseband signal components I and Q) of a center frequencyFif1=0[Hz] to a target signal band. The roll-off filter 41 includes areal filter 41 a and an imaginary filter 41 b.

[0108] A frequency converter 42 frequency-converts an output signal fromthe roll-off filter 41 to obtain a complex signal of a center frequencyFif2. The frequency converter 42 includes a local oscillator 42 a usingthe NCO of the first embodiment, for generating a complex local signalof a frequency Fc1 (containing a real component “C1(t)=cos(2π×Fc1×t)”and an imaginary component “S1(t)=sin(2π×Fc1×t)” whose phase is 90degrees delayed from that of the real component), and multipliers 42 b,42 c, 42 d and 42 e, a subtracter 42 f and an adder 42 g for performingmultiplication, subtraction and addition operations with respect to theoutput signal from the roll-off filter 41 and the complex local signalgenerated by the local oscillator 42 a, respectively.

[0109] An interpolator 43 interpolates the complex signal from thefrequency converter 42. To this end, the interpolator 43 includes realand imaginary interpolators 43 a and 43 b each for multiplying asampling frequency Fs1 of a corresponding one of real and imaginarycomponents of the complex signal by N to convert it into a samplingfrequency Fs2=Fs1×N. A frequency converter 44 frequency-converts anoutput signal from the interpolator 43 to output a real signal of atarget center frequency Fif3. The frequency converter 44 includes alocal oscillator 44 a using the NCO of the first embodiment, forgenerating a complex local signal of a frequency Fc2 (containing a realcomponent “C2(t)=cos(2π×Fc2×t)” and an imaginary component“S2(t)=sin(2π×Fc2×t)” whose phase is 90 degrees delayed from that of thereal component), multipliers 44 b and 44 c for multiplying real andimaginary components of the output signal from the interpolator 43 bythe real and imaginary components of the complex local signal generatedby the local oscillator 44 a, respectively, and a subtracter 44 d forsubtracting output signals from the multipliers 44 b and 44 c from eachother.

[0110] For example, assuming that a desired frequency setting intervalFD of an output signal is above a frequency setting interval FD2 of thefrequency converter 44 and is indivisible by it, the digitalup-converter is operated in the following manner. In this case, if K1,K2, and L2 are arbitrary integers, the frequency converter 42 sets phasedifference data φ1 to the local oscillator 42 a using the NCO of thefirst embodiment to a value of φ1=Fc1/FD1=Fc1/(FD mod FD2)×K1. Then, thefrequency converter 42 converts a baseband signal of a center frequencyFif1 into a complex signal of a center frequency Fif2 using a complexlocal signal of a frequency Fc1 output from the local oscillator 42 aand set to a frequency setting interval of an FD1 step, where FD1=(FDmod FD2)/K1. The local oscillator 42 a outputs the complex local signalof the frequency Fc1 by accumulating the phase difference data by amodulo operation taking the nearest integer of M1 as a modulus, whereM1=Fs2/(FD mod FD2)×K1.

[0111] Also, the frequency converter 44 sets phase difference data φ2 tothe local oscillator 44 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/FD×K2/L2. The frequency converter 44 convertsthe complex signal of the center frequency Fif2 into a complex signal ofa center frequency Fif3 using a complex local signal of a frequency Fc2output from the local oscillator 44 a and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2×L2. Here, the local oscillator44 a outputs the complex local signal of the frequency Fc2 byaccumulating the phase difference data by a modulo operation taking thenearest integer of M2 as a modulus, where M2=Fs2/FD×K2/L2.

[0112] However, for example, assuming that a desired frequency settinginterval FD of an output signal is below a frequency setting intervalFD2 of the frequency converter 44 and FD2 is indivisible by FD, thefrequency converter 42 sets phase difference data φ1 to the localoscillator 42 a using the NCO of the first embodiment to a value ofφ1=Fc1/FD1=Fc1/(FD2 mod FD)×K1. The frequency converter 42 converts abaseband signal of a center frequency Fif1 into a complex signal of acenter frequency Fif2 using a complex local signal of a frequency Fc1output from the local oscillator 42 a and set to a frequency settinginterval of an FD1 step, where FD1=(FD2 mod FD)/K1. Here, the localoscillator 42 a outputs the complex local signal of the frequency Fc1 byaccumulating the phase difference data by a modulo operation taking thenearest integer of M1 as a modulus, where M1=Fs2/(FD2 mod FD)×K1.

[0113] Also, the frequency converter 44 sets phase difference data φ2 tothe local oscillator 44 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/FD×K2/L2. Then, the frequency converter 44converts the complex signal of the center frequency Fif2 into a complexsignal of a center frequency Fif3 using a complex local signal of afrequency Fc2 output from the local oscillator 44 a and set to afrequency setting interval of an FD2 step, where FD2=FD/K2×L2. The localoscillator 44 a outputs the complex local signal of the frequency Fc2 byaccumulating the phase difference data by a modulo operation taking thenearest integer of M2 as a modulus, where M2=Fs2/FD×K2/L2.

[0114] Alternatively, for example, assuming that a desired frequencysetting interval FD of an output signal is higher than or equal to afrequency setting interval FD2 of the frequency converter 44 and isevenly divisible by it, or that FD is lower than FD2 and FD2 is evenlydivisible by FD, the digital up-converter is operated in the followingmanner. In this case, the frequency converter 42 sets phase differencedata φ1 to the local oscillator 42 a using the NCO of the firstembodiment to a value of φ1=Fc1/FD1=Fc1/FD×K1. The frequency converter42 converts a baseband signal of a center frequency Fif1 into a complexsignal of a center frequency Fif2 using a complex local signal of afrequency Fc1 output from the local oscillator 42 a and set to afrequency setting interval of an FD1 step, where FD1=FD/K1. Here, thelocal oscillator 42 a outputs the complex local signal of the frequencyFc1 by accumulating the phase difference data by a modulo operationtaking the nearest integer of M1 as a modulus, where M1=Fs2/FD×K1.

[0115] Also, the frequency converter 44 sets phase difference data φ2 tothe local oscillator 44 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/FD×K2/L2. Then, the frequency converter 44converts the complex signal of the center frequency Fif2 into a complexsignal of a center frequency Fif3 using a complex local signal of afrequency Fc2 output from the local oscillator 44 a and set to afrequency setting interval of an FD2 step, where FD2=FD/K2×L2. The localoscillator 44 a outputs the complex local signal of the frequency Fc2 byaccumulating the phase difference data by a modulo operation taking thenearest integer of M2 as a modulus, where M2=Fs2/FD×K2/L2.

[0116] However, in the case where a multiple of the frequency settinginterval FD2 of the frequency converter 44 is equal to that of thefrequency setting interval FD of the output signal, the digitalup-converter with the above-described configuration can set thefrequency setting interval of its output signal to FD by means of onlythe frequency converter 44. In this case, the frequency conversion bythe frequency converter 42 may be stopped.

[0117] In the digital-up converter of the present embodiment, in thecase where the frequency setting interval FD2 of the frequency converter44 is settable at a step lower than or equal to the desired frequencysetting interval FD of the output signal, each frequency can be input bymerely changing the setting of frequency data (phase difference data) tothe NCO of the frequency converter 44. Therefore, a data setting time ofa controller that controls the digital up-converter can be reduced byhalf compared with a conventional digital up-converter requiring thesetting of data to both frequency converters and the frequency data tothe NCO can be computed in a simpler manner.

[0118]FIG. 7 is a block diagram illustrating the configuration of anembodiment of a receiver using the NCO of the first embodiment. Asillustrated in FIG. 7, the receiver comprises a local oscillator 51including the NCO 51 a of the first embodiment, a digital to analogconverter (DAC) 51 b for digital/analog-converting an output signal fromthe NCO 51 a, and a PLL circuit 51 c for receiving an output signal fromthe DAC 51 b as a reference signal. The receiver further comprises amixer 52 for frequency-converting a received signal (real signal) of acenter frequency Frf into an analog intermediate frequency (IF) signalof a center frequency Fifa on the basis of an analog local signal (realsignal “C(t)=cos(2π×Fcp×t)”) of a frequency Fcp output from the localoscillator 51.

[0119] Assuming that a multiplication ratio of the PLL circuit 51 c is Pand an output frequency of the NCO 51 a is Fc1, the local oscillator 51outputs an analog local signal of a frequency Fcp=Frf−Fifa=Fc1×P. Also,a frequency setting step FDP of the analog local signal (frequencysetting interval of the mixer 52) is a multiplication of a frequencysetting step FD of the NCO 51 a by P.

[0120] A band pass filter 53 has a pass frequency band characteristiccorresponding to a frequency band of the analog IF signal and acts toextract the analog IF signal from the mixer 52 and output it to ananalog to digital converter (ADC) 54.

[0121] The ADC 54 quantizes the analog IF signal from the band passfilter 53 and generates a “Sub-Nyquist sampled” digital IF signal of acenter frequency Fif2.

[0122] The digital down-converter 11 of FIG. 3 is used to convert anoutput signal from the ADC 54 into a complex signal (I,Q) of a frequencydesired by a demodulator 55 and output the converted complex signal tothe demodulator 55. The demodulator 55 demodulates the output signalfrom the digital down-converter 11 to extract received data therefrom.

[0123] For example, assuming that a desired frequency setting intervalFD of a received signal is above a frequency setting interval FDP of themixer 52 and is indivisible by it, the receiver is operated in thefollowing manner. In this case, if K1, K2 and L1 are arbitrary integers,the mixer 52 sets phase difference data φ1 to the NCO 51 a of the firstembodiment operating at a sampling frequency Fs to a value ofφ1=Fc1/FD1=Fc1/FD×K1/L1. The mixer 52 converts a received signal of acenter frequency Frf into an analog IF signal of a center frequency Fifausing an analog local signal of a frequency Fcp output from the localoscillator 51 and set to a frequency setting interval of an FDP step,where FDP=FD/K1×L1. Here, the local oscillator 51 outputs the analoglocal signal of the frequency Fcp by accumulating the phase differencedata by a modulo operation taking the nearest integer of M1 as amodulus, where M1=Fs/FD×K1/L1×P.

[0124] Also, the frequency converter 12 sets phase difference data φ2 tothe local oscillator 12 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/(FD mod FDP)×K2. Then, the frequency converter12 converts a digital IF signal of a center frequency Fif2 and samplingfrequency Fs1, generated by Sub-Nyquist sampling the analog IF signal ofthe center frequency Fifa by the ADC 54, into a complex signal of afrequency desired by the demodulator 55 using a complex local signal ofa frequency Fc2 output from the local oscillator 12 a and set to afrequency setting interval of an FD2 step, where FD2=(FD mod FDP)/K2.The local oscillator 12 a outputs the complex local signal of thefrequency Fc2 by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs1/(FD mod FDP)×K2.

[0125] However, for example, assuming that a desired frequency settinginterval FD of a received signal is below a frequency setting intervalFDP of the mixer 52 and FDP is indivisible by FD, the mixer 52 setsphase difference data φ1 to the NCO 51 a of the first embodimentoperating at a sampling frequency Fs to a value ofφ1=Fc1/FD1=Fc1/FD×K1/L1. The mixer 52 converts a received signal of acenter frequency Frf into an analog IF signal of a center frequency Fifausing an analog local signal of a frequency Fcp output from the localoscillator 51 and set to a frequency setting interval of an FDP step,where FDP=FD/K1×L1. Here, the local oscillator 51 outputs the analoglocal signal of the frequency Fcp by accumulating the phase differencedata by a modulo operation taking the nearest integer of M1 as amodulus, where M1=Fs/FD×K1/L1×P.

[0126] Also, the frequency converter 12 sets phase difference data φ2 tothe local oscillator 12 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/(FDP mod FD)×K2. The frequency converter 12converts a digital IF signal of a center frequency Fif2 and samplingfrequency Fs1, generated by Sub-Nyquist sampling the analog IF signal ofthe center frequency Fifa by the ADC 54, into a complex signal of afrequency desired by the demodulator 55 using a complex local signal ofa frequency Fc2 output from the local oscillator 12 a and set to afrequency setting interval of an FD2 step, where FD2=(FDP mod FD)/K2.The local oscillator 12 a outputs the complex local signal of thefrequency Fc2 by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs1/(FDP mod FD)×K2.

[0127] Alternatively, for example, assuming that a desired frequencysetting interval FD of a received signal is higher than or equal to afrequency setting interval FDP of the mixer 52 and is evenly divisibleby it, or that FD is lower than FDP and FDP is evenly divisible by FD,the mixer 52 sets phase difference data φ1 to the NCO 51 a of the firstembodiment operating at a sampling frequency Fs to a value ofφ1=Fc1/FD1=Fc1/FD×K1/L1. The mixer 52 converts a received signal of acenter frequency Frf into an analog IF signal of a center frequency Fifausing an analog local signal of a frequency Fcp output from the localoscillator 51 and set to a frequency setting interval of an FDP step,where FDP=FD/K1×L1. The local oscillator 51 outputs the analog localsignal of the frequency Fcp by accumulating the phase difference data bya modulo operation taking the nearest integer of M1 as a modulus, whereM1=Fs/FD×K1/L1×P.

[0128] Also, the frequency converter 12 sets phase difference data φ2 tothe local oscillator 12 a using the NCO of the first embodiment to avalue of φ2=Fc2/FD2=Fc2/FD×K2. Then, the frequency converter 12 convertsa digital IF signal of a center frequency Fif2 and sampling frequencyFs1, generated by Sub-Nyquist sampling the analog IF signal of thecenter frequency Fifa by the ADC 54, into a complex signal of afrequency desired by the demodulator 55 using a complex local signal ofa frequency Fc2 output from the local oscillator 12 a and set to afrequency setting interval of an FD2 step, where FD2=FD/K2. Here, thelocal oscillator 12 a outputs the complex local signal of the frequencyFc2 by accumulating the phase difference data by a modulo operationtaking the nearest integer of M2 as a modulus, where M2=Fs1/FD×K2.

[0129] On the other hand, in the case where a multiple of the frequencysetting interval FDP of the mixer 52 is equal to that of the frequencysetting interval FD of the received signal, the receiver with theabove-described configuration can convert the frequency of the receivedsignal input thereto at the frequency setting interval FD into thatdesired by the demodulator 55 by means of only the mixer 52. In thiscase, the frequency conversion by the frequency converter 12 may bestopped.

[0130] Further, the receiver with the above-stated configuration canhave various settings of the respective parameters as shown in the belowtables 6 to 9. The tables 6 and 7 show examples of settings of therespective parameters in a W-CDMA system, the table 8 shows examples ofsettings of the respective parameters in an IS-95 Band (Class 0 system,and the table 9 shows examples of settings of the respective parametersin an IEEE 802.11a system. TABLE 6 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz][MHz] P [KHz] [KHz] [MHz] [KHz] [MHz] K1 L1 1 2257.50 2068.00 200 200.04000.0 61.440 20.0 10.340 1 20 2 2257.50 2068.00 100 200.0 4000.0 92.16040.0 20.680 1 20 3 2257.50 2068.00 100 200.0 4000.0 122.880 40.0 20.6801 20 4 2247.50 2060.00 100 200.0 5000.0 153.600 50.0 20.600 1 25 52252.50 2065.00 100 200.0 5000.0 153.600 50.0 20.650 1 25 6 2257.502070.00 100 200.0 5000.0 153.600 50.0 20.700 1 25 7 2257.52 2070.00 100200.0 5000.0 153.600 50.0 20.700 1 25 8 2262.50 2075.00 100 200.0 5000.0153.600 50.0 20.750 1 25 9 2262.54 2075.00 100 200.0 5000.0 153.600 50.020.750 1 25 10 2267.50 2080.00 100 200.0 5000.0 153.600 50.0 20.800 1 2511 2257.50 2066.40 128 200.0 2400.0 153.600 18.8 16.144 1 12 12 2257.502066.40 128 200.0 2400.0 153.600 18.8 16.144 1 12 13 2257.50 2066.40 128200.0 2400.0 153.600 18.8 16.144 1 12 14 2257.50 2070.00 50 200.0 5000.0150.000 100.0 41.400 1 25

[0131] TABLE 7 Fifa Fif2 Fs1 FD2 Fc2 No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz][MHz] K2 M2 ΔØ2 1 3072 517 189.50 35.90 153.6 100.000 35.90 2 1536 359 22304 517 189.50 35.90 153.6 100.000 35.90 2 1536 359 3 3072 517 189.5035.90 153.6 100.000 35.90 2 1536 359 4 3072 412 187.50 33.90 153.6100.000 33.90 2 1536 339 5 3072 413 187.50 33.90 153.6 100.000 33.90 21536 339 6 3072 414 187.50 33.90 153.6 100.000 33.90 2 1536 339 7 3072414 187.52 33.92 153.6 20.000 33.92 10 7680 1696 8 3072 415 187.50 33.90153.6 100.000 33.90 2 1536 339 9 3072 415 187.54 33.94 153.6 20.00033.94 10 7680 1697 10 3072 416 187.50 33.90 153.6 100.000 33.90 2 1536339 11 8192 861 191.10 37.50 153.6 100.000 37.50 2 1536 375 12 8192 861191.10 37.50 153.6 100.000 37.50 2 1536 375 13 8192 861 191.10 37.50153.6 100.000 37.50 2 1536 375 14 1500 414 187.50 33.90 153.6 100.00033.90 2 1536 339

[0132] TABLE 8 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz] [MHz] P [KHz] [KHz][MHz] [KHz] [MHz] K1 L1 1 869.97 679.68 50 30.0 960.0 98.304 19.2 13.5941 32 2 870.00 679.68 50 30.0 960.0 98.304 19.2 13.594 1 32 3 870.03679.68 50 30.0 960.0 98.304 19.2 13.594 1 32 4 869.97 679.68 50 30.0960.0 157.286 19.2 13.594 1 32 5 870.00 679.68 50 30.0 960.0 157.28619.2 13.594 1 32 6 870.03 679.68 50 30.0 960.0 157.286 19.2 13.594 1 32Fifa Fif2 Fs1 FD2 Fc2 No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz] [MHz] K2 M2 ΔØ21 5120 708 190.29 33.00 157.286 3.750 33.00 8 41943 8801 2 5120 708190.32 33.03 157.286 3.750 33.03 8 41943 8809 3 5120 708 190.35 33.06157.286 3.750 33.06 8 41943 8817 4 8192 708 190.29 33.00 157.286 3.75033.00 8 41943 8801 5 8192 708 190.32 33.03 157.286 3.750 33.03 8 419438809 6 8192 708 190.35 33.06 157.286 3.750 33.06 8 41943 8817

[0133] TABLE 9 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz] [MHz] P [KHz] [KHz][MHz] [KHz] [MHz] K1 L1 1 5200.00 5010.00 200 100.0 10000.0 100.0 50.025.050 1 100 2 5180.00 4990.00 128 200.0 10000.0 200.0 78.1 38.984 1 503 5200.00 5010.00 128 200.0 10000.0 200.0 78.1 39.141 1 50 4 5220.005030.00 128 200.0 10000.0 200.0 78.1 39.297 1 50 Fifa Fif2 Fs1 FD2 Fc2No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz] [MHz] K2 M2 ΔØ2 1 2000 501 190.00−10.00 100 100.000 −10.00 1 1000 −100 2 2560 499 190.00 −10.00 200200.000 −10.00 1 1000 −50 3 2560 501 190.00 −10.00 200 200.000 −10.00 11000 −50 4 2560 503 190.00 −10.00 200 200.000 −10.00 1 1000 −50

[0134] In the receiver of the present embodiment, where the frequencysetting interval FDP of the mixer 52 is settable at a step lower than orequal to the desired frequency setting interval FD of the receivedsignal, each frequency can be input by merely changing the setting offrequency data (phase difference data) to the NCO of the localoscillator 51. Therefore, a data setting time of a controller thatcontrols the receiver can be reduced compared with a conventionalreceiver and the frequency data to the NCO can be computed in a simplermanner.

[0135]FIG. 8 is a block diagram illustrating the configuration of analternative embodiment of the receiver using the NCO of the firstembodiment, wherein a quadrature demodulator 82 is used instead of themixer 52 of the receiver illustrated in FIG. 7 to quadrature-demodulatean analog version of a received signal. Referring to FIG. 8, thereceiver comprises a local oscillator 81 including the NCO 81 a of thefirst embodiment, a DAC 81 b for digital/analog-converting an outputsignal from the NCO 81 a, and a PLL circuit 81 c for receiving an outputsignal from the DAC 81 b as a reference signal. The quadraturedemodulator 82 frequency-converts a received signal (real signal) of acenter frequency Frf into an analog IF complex signal of a centerfrequency Fifa on the basis of an analog local signal (containing a realcomponent “C1(t)=cos(2π×Fcp×t)” and an imaginary component“−S1(t)=−sin(2π×Fcp×t)” whose phase is 90 degrees ahead of that of thereal component) of a frequency Fcp output from the local oscillator 81.To this end, the quadrature demodulator 82 includes a real mixer 82 aand an imaginary mixer 82 b.

[0136] Assuming that a multiplication ratio of the PLL circuit 81 c is Pand an output frequency of the NCO 81 a is Fc1, the local oscillator 81outputs an analog local signal of a frequency Fcp=Frf−Fifa=Fc1×P. Also,a frequency setting step FDP of the analog local signal (frequencysetting interval of the quadrature demodulator 82) is a multiplicationof a frequency setting step FD of the NCO 81 a by P.

[0137] A band pass filter 83 has a pass frequency band characteristiccorresponding to a frequency band of the analog IF complex signal andacts to extract the analog IF complex signal from the quadraturedemodulator 82 and output it to an ADC 84. To this end, the band passfilter 83 includes a real band pass filter 83 a and an imaginary bandpass filter 83 b.

[0138] The ADC 84 quantizes the analog IF complex signal from the bandpass filter 83 and generates a digital IF signal of a center frequencyFif2. The ADC 84 includes a real ADC 84 a and an imaginary ADC 84 b.

[0139] A frequency converter 85 frequency-converts an output signal fromthe ADC 84. The frequency converter 85 includes a local oscillator 85 ausing the NCO of the first embodiment, for generating a complex localsignal of a frequency Fc2 (containing a real component“C2(t)=cos(2π×Fc2×t)” and an imaginary component “−S2(t)=−sin(2π×Fc2×t)”whose phase is 90 degrees ahead of that of the real component), andmultipliers 85 b, 85 c, 85 d, and 85 e, a subtracter 85 f and an adder85 g for performing multiplication, subtraction and addition operationswith respect to the output signal from the ADC 84 and the complex localsignal generated by the local oscillator 85 a, respectively.

[0140] A decimator 86 decimates a complex signal from the frequencyconverter 85. The decimator 86 includes real and imaginary decimators 86a and 86 b each for multiplying a sampling frequency Fs1 of acorresponding one of real and imaginary components of the complex signalby 1/N to convert it into a sampling frequency Fs2=Fs1/N. A roll-offfilter 87 band-limits an output signal from the decimator 86 to a targetsignal band and outputs the resulting complex signal (I,Q) of thefrequency desired by the demodulator 55 thereto. The roll-off filter 87includes a real filter 87 a and an imaginary filter 87 b.

[0141] In the above-described receiver, the NCO 81 a, local oscillator81, local oscillator 85 a and frequency converter 85 perform the sameoperations as those of the NCO 51 a, local oscillator 51, localoscillator 12 a and frequency converter 12 in the receiver previouslystated with reference to FIG. 7 on the basis of the relations betweenthe desired frequency setting interval FD of the received signal and thefrequency setting interval FDP of the quadrature demodulator 82,respectively.

[0142] However, in the case where a multiple of the frequency settinginterval FDP of the quadrature demodulator 82 is equal to that of thefrequency setting interval FD of the received signal, the receiver withthe above-described configuration can convert the frequency of thereceived signal input thereto at the frequency setting interval FD intothat desired by the demodulator by means of only the quadraturedemodulator 82. In this case, the frequency conversion by the frequencyconverter 85 may be stopped.

[0143] Further, the receiver with the above-stated configuration canhave various settings of the respective parameters as shown in the belowtables 10 to 13. The tables 10 and 11 show examples of settings of therespective parameters in a W-CDMA system, the table 12 shows examples ofsettings of the respective parameters in an IS-95 Band (Class 0) system,and the table 13 shows examples of settings of the respective parametersin an IEEE 802.11a system TABLE 10 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz][MHz] P [KHz] [KHz] [MHz] [KHz] [MHz] K1 L1 1 2257.50 2256.00 200.0200.0 4000.0 61.440 20.0 11.280 1 20 2 2257.50 2256.00 100.0 200.04000.0 92.160 40.0 22.560 1 20 3 2257.50 2256.00 100.0 200.0 4000.0122.880 40.0 22.560 1 20 4 2247.50 2250.00 100.0 200.0 5000.0 153.60050.0 22.500 1 25 5 2252.50 2255.00 100.0 200.0 5000.0 153.600 50.022.550 1 25 6 2257.50 2260.00 100.0 200.0 5000.0 153.600 50.0 22.600 125 7 2257.52 2260.00 100.0 200.0 5000.0 153.600 50.0 22.600 1 25 82262.50 2265.00 100.0 200.0 5000.0 153.600 50.0 22.650 1 25 9 2262.542265.00 100.0 200.0 5000.0 153.600 50.0 22.650 1 25 10 2267.50 2270.00100.0 200.0 5000.0 153.600 50.0 22.700 1 25 11 2257.50 2258.40 128.0200.0 2400.0 153.600 18.8 17.644 1 12 12 2257.50 2258.40 128.0 200.02400.0 153.600 18.8 17.644 1 12 13 2257.50 2258.40 128.0 200.0 2400.0153.600 18.8 17.644 1 12 14 2257.50 2260.00 50.0 200.0 5000.0 150.000100.0 45.200 1 25

[0144] TABLE 11 Fifa Fif2 Fs1 FD2 Fc2 No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz][MHz] K2 M2 ΔØ2 1 3072 564 1.50 1.50 30.72 25.000 1.50 8 1229 60 2 2304564 1.50 1.50 30.72 25.000 1.50 8 1229 60 3 3072 564 1.50 1.50 30.7225.000 1.50 8 1229 60 4 3072 450 −2.50 −2.50 30.72 20.000 −2.50 10 1536−125 5 3072 451 −2.50 −2.50 30.72 20.000 −2.50 10 1536 −125 6 3072 452−2.50 −2.50 30.72 20.000 −2.50 10 1536 −125 7 3072 452 −2.48 −2.48 30.7220.000 −2.48 10 1539 −124 8 3072 453 −2.50 −2.50 30.72 20.000 −2.50 101536 −125 9 3072 453 −2.46 −2.46 30.72 20.000 −2.46 10 1536 −123 10 3072454 −2.50 −2.50 30.72 20.000 −2.50 10 1536 −125 11 8192 941 −0.90 −0.9030.72 33.333 −0.90 6 922 −27 12 8192 941 −0.90 −0.90 30.72 33.333 −0.906 922 −27 13 8192 941 −0.90 −0.90 30.72 33.333 −0.90 6 922 −27 14 1500452 −2.50 −2.50 30.72 20.000 −2.50 10 1536 −125

[0145] TABLE 12 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz] [MHz] P [KHz] [KHz][MHz] [KHz] [MHz] K1 L1 1 869.97 869.76 50 30.0 960.0 98.304 19.2 17.3951 32 2 870.00 869.76 50 30.0 960.0 98.304 19.2 17.395 1 32 3 870.03869.76 50 30.0 960.0 98.304 19.2 17.395 1 32 4 869.97 869.76 50 30.0960.0 157.286 19.2 17.395 1 32 5 870.00 869.76 50 30.0 960.0 157.28619.2 17.395 1 32 6 870.03 869.76 50 30.0 960.0 157.286 19.2 17.395 1 32Fifa Fif2 Fs1 FD2 Fc2 No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz] [MHz] K2 M2 ΔØ21 5120 906 0.21 0.21 9.8304 30.000 0.21 1 328 7 2 5120 906 0.24 0.249.8304 30.000 0.24 1 328 8 3 5120 906 0.27 0.27 9.8304 30.000 0.27 1 3289 4 8192 906 0.21 0.21 9.8304 30.000 0.21 1 328 7 5 8192 906 0.24 0.249.8304 30.000 0.24 1 328 8 6 8192 906 0.27 0.27 9.8304 30.000 0.27 1 3289

[0146] TABLE 13 Frf Fcp FD FDP Fs FD1 Fc1 No. [MHz] [MHz] P [KHz] [KHz][MHz] [KHz] [MHz] K1 L1 1 5200.00 5200.00 200 100.0 10000.0 100.0 50.026.000 1 100  2 5180.00 5180.00 128 200.0 10000.0 200.0 78.1 40.469 1 503 5200.00 5200.00 128 200.0 10000.0 200.0 78.1 40.625 1 50 4 5220.005220.00 128 200.0 10000.0 200.0 78.1 40.781 1 50 Fifa Fif2 Fs1 FD2 Fc2No. M1 ΔØ1 [MHz] [MHz] [MHz] [KHz] [MHz] K2 M2 ΔØ2 1 2000 520 0.00 0.00100 — — — — — 2 2560 518 0.00 0.00 200 — — — — — 3 2560 520 0.00 0.00200 — — — — — 4 2560 522 0.00 0.00 200 — — — — —

[0147] In the receiver of the present embodiment, in the case where thefrequency setting interval FDP of the quadrature demodulator 82 issettable at a step lower than or equal to the desired frequency settinginterval FD of the received signal, each frequency can be input bymerely changing the setting of frequency data (phase difference data) tothe NCO of the local oscillator 81. Therefore, a data setting time of acontroller that controls the receiver can be reduced compared with aconventional receiver and the frequency data to the NCO can be computedin a simpler manner.

[0148] Further, in the receiver of the present embodiment, the centerfrequency Fifa of the analog IF complex signal can be set to a lowervalue, thereby making it possible to apply a relatively small number ofphase amplitude data to the local oscillator 85 a using the NCO of thefirst embodiment, constructing the downstream frequency converter 85.

[0149] The NCO of the first embodiment may also be used in a transmitteras shown in FIG. 9. FIG. 9 is a block diagram illustrating theconfiguration of a transmitter using the NCO of the first embodiment. Asillustrated in FIG. 9, the transmitter comprises a modulator 61 formodulating a carrier based on transmit data to be transmitted from thetransmitter, and a roll-off filter 62 for band-limiting a complex signal(containing baseband signal components I and Q) output from themodulator 61 to a target signal band. The roll-off filter 62 includes areal filter 62 a and an imaginary filter 62 b.

[0150] A frequency converter 63 frequency-converts an output signal fromthe roll-off filter 62 to obtain a complex signal of a center frequencyFif2. The frequency converter 63 includes a local oscillator 63 a usingthe NCO of the first embodiment, for generating a complex local signalof a frequency Fc1=Fif2 (containing a real component“C1(t)=cos(2π×Fc1×t)” and an imaginary component “S1(t)=sin(2π×Fc1×t)”whose phase is 90 degrees delayed from that of the real component), andmultipliers 63 b, 63 c, 63 d and 63 e, a subtracter 63 f and an adder 63g for performing multiplication, subtraction and addition operationswith respect to the output signal from the roll-off filter 62 and thecomplex local signal generated by the local oscillator 63 a,respectively.

[0151] An interpolation band pass filter 68 interpolates and band passfilters the complex signal from the frequency converter 63. Theinterpolation band pass filter 68 includes real and imaginaryinterpolators 64 a and 64 b each for multiplying a sampling frequencyFs1 of a corresponding one of real and imaginary components of thecomplex signal by N to convert it into a sampling frequency Fs2=Fs1×N.The interpolation band pass filter 68 further includes multipliers 66 aand 66 b for multiplying a real component “C2(t)=cos(2π×Fc2×t)” and animaginary component “S2(t)=sin(2π×Fc2×t)” whose phase is 90 degreesdelayed from that of the real component, contained in an output signalfrom the NCO 70 a of the first embodiment, by a filter coefficient of alow pass filter 65, respectively, and real and imaginary band passfilters 67 a and 67 b, a subtracter 67 c and an adder 67 d forperforming band pass filtering, subtraction and addition operations withrespect to output signals from the interpolators 64 a and 64 b on thebasis of output signals from the multipliers 66 a and 66 b,respectively.

[0152] A real DAC 69 a and imaginary DAC 69 b cooperate to convert adigital signal of the center frequency Fif2 from the interpolation bandpass filter 68 into a complex analog IF signal of a center frequencyFifa.

[0153] A local oscillator 70 includes the NCO 70 a of the firstembodiment, a DAC 70 b for digital/analog-converting an output signalfrom the NCO 70 a, and a PLL circuit 70 c for receiving an output signalfrom the DAC 70 b as a reference signal. A quadrature modulator 71frequency-converts the complex analog IF signal of the center frequencyFifa from the real DAC 69 a and imaginary DAC 69 b to output a transmitsignal (real signal) of a target center frequency Frf. The quadraturemodulator 71 includes multipliers 71 a and 71 b for multiplying real andimaginary components of the complex analog IF signal from the real DAC69 a and imaginary DAC 69 b by a real component “C3(t)=cos(2π×Fcp×t)”and an imaginary component “S3(t)=sin(2π×Fcp×t)” whose phase is 90degrees delayed from that of the real component, contained in a complexanalog local signal of a frequency Fcp output from the local oscillator70, respectively, and a subtracter 71 c for subtracting output signalsfrom the multipliers 71 a and 71 b from each other.

[0154] Assuming that a multiplication ratio of the PLL circuit 70 c is Pand an output frequency of the NCO 70 a is Fc2, the local oscillator 70outputs an analog local signal of a frequency Fcp=Frf−Fifa=Fc2×P. Also,a frequency setting step FDP of the analog local signal (frequencysetting interval of the quadrature modulator 71) is a multiplication ofa frequency setting step FD of the NCO 70 a by P.

[0155] For example, assuming that a desired frequency setting intervalFD of a transmit signal is above a frequency setting interval FDP of thequadrature modulator 71 and is indivisible by it; the transmitter isoperated in the following manner. In this case, if K1, K2 and L2 arearbitrary integers, the frequency converter 63 sets phase differencedata φ1 to the local oscillator 63 a using the NCO of the firstembodiment to a value of φ1=Fc1/FD1=Fc1/(FD mod FDP)×K1. The frequencyconverter 63 converts a complex signal (containing baseband signalcomponents I and Q) of a sampling frequency Fs1 output from themodulator 61 into a complex signal of a center frequency Fif2 using acomplex local signal of a frequency Fc1 output from the local oscillator63 a and set to a frequency setting interval of an FD1 step, whereFD1=(FD mod FDP)/K1. Here, the local oscillator 63 a outputs the complexlocal signal of the frequency Fc1 by accumulating the phase differencedata by a modulo operation taking the nearest integer of M1 as amodulus, where M1=Fs1/(FD mod FDP)×K1.

[0156] Also, the quadrature modulator 71 sets phase difference data φ2to the NCO 70 a of the first embodiment operating at a samplingfrequency Fs to a value of φ2=Fc2/FDP=Fc2/FD×K2/L2. The quadraturemodulator 71 converts an analog IF signal of a center frequency Fifa,generated by digital/analog-converting a digital IF signal of the centerfrequency Fif2 by the real DAC 69 a and imaginary DAC 69 b, into atransmit signal (real signal) of a target center frequency Frf using ananalog local signal of a frequency Fcp output from the local oscillator70 and set to a frequency setting interval of an FDP step, whereFDP=FD/K2×L2. The local oscillator 70 outputs the analog local signal ofthe frequency Fcp by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs/FD×K2/L2×P.

[0157] However, for example, assuming that a desired frequency settinginterval FD of a transmit signal is below a frequency setting intervalFDP of the quadrature modulator 71 and FDP is indivisible by FD, thefrequency converter 63 sets phase difference data φ1 to the localoscillator 63 a using the NCO of the first embodiment to a value ofφ1=Fc1/FD1=Fc1/(FDP mod FD)×K1. Then, the frequency converter 63converts a complex signal (containing baseband signal components I andQ) of a sampling frequency Fs1 output from the modulator 61 into acomplex signal of a center frequency Fif2 using a complex local signalof a frequency Fc1 output from the local oscillator 63 a and set to afrequency setting interval of an FD1 step, where FD1=(FDP mod FD)/K1.Here, the local oscillator 63 a outputs the complex local signal of thefrequency Fc1 by accumulating the phase difference data by a modulooperation taking the nearest integer of M1 as a modulus, whereM1=Fs1/(FDP mod FD)×K1.

[0158] Also, the quadrature modulator 71 sets phase difference data φ2to the NCO 70 a of the first embodiment operating at a samplingfrequency Fs to a value of φ2=Fc2/FDP=Fc2/FD×K2/L2. Then, the quadraturemodulator 71 converts an analog IF signal of a center frequency Fifa,generated by digital/analog-converting a digital IF signal of the centerfrequency Fif2 by the real DAC 69 a and imaginary DAC 69 b, into atransmit signal (real signal) of a target center frequency Frf using ananalog local signal of a frequency Fcp output from the local oscillator70 and set to a frequency setting interval of an FDP step, whereFDP=FD/K2×L2. The local oscillator 70 outputs the analog local signal ofthe frequency Fcp by accumulating the phase difference data by a modulooperation taking the nearest integer of M2 as a modulus, whereM2=Fs/FD×K2/L2×P.

[0159] Alternatively, for example, assuming that a desired frequencysetting interval FD of a transmit signal is higher than or equal to afrequency setting interval FDP of the quadrature modulator 71 and isevenly divisible by it, or that FD is lower than FDP and FDP is evenlydivisible by FD, the transmitter is operated in the following manner. Inthis case, the frequency converter 63 sets phase difference data φ1 tothe local oscillator 63 a using the NCO of the first embodiment to avalue of φ1=Fc1/FD1=Fc1/FD×K1. The frequency converter 63 converts acomplex signal (containing baseband signal components I and Q) of asampling frequency Fs1 output from the modulator 61 into a complexsignal of a center frequency Fif2 using a complex local signal of afrequency Fc1 output from the local oscillator 63 a and set to afrequency setting interval of an FD1 step, where FD1=FD/K1. Here, thelocal oscillator 63 a outputs the complex local signal of the frequencyFc1 by accumulating the phase difference data by a modulo operationtaking the nearest integer of M1 as a modulus, where M1=Fs1/FD×K1.

[0160] Also, the quadrature modulator 71 sets phase difference data φ2to the NCO 70 a of the first embodiment operating at a samplingfrequency Fs to a value of φ2=Fc2/FDP=Fc2/FD×K2/L2. Then, the quadraturemodulator 71 converts an analog IF signal of a center frequency Fifa,generated by digital/analog-converting a digital IF signal of the centerfrequency Fif2 by the real DAC 69 a and imaginary DAC 69 b, into atransmit signal (real signal) of a target center frequency Frf using ananalog local signal of a frequency Fcp output from the local oscillator70 and set to a frequency setting interval of an FDP step, whereFDP=FD/K2×L2. Here, the local oscillator 70 outputs the analog localsignal of the frequency Fcp by accumulating the phase difference data bya modulo operation taking the nearest integer of M2 as a modulus, whereM2=Fs/FD×K2/L2×P.

[0161] However, in the case where a multiple of the frequency settinginterval FDP of the quadrature modulator 71 is equal to that of thefrequency setting interval FD of the transmit signal, the transmitterwith the above-described configuration can frequency-convert thetransmit signal into the transmit signal (real signal) of the targetcenter frequency Frf by means of only the quadrature modulator 71. Inthis case, the frequency conversion by the frequency converter 63 may bestopped.

[0162] In the transmitter of the present embodiment, in the case wherethe frequency setting interval FDP of the quadrature modulator 71 issettable at a step lower than or equal to the desired frequency settinginterval FD of the transmit signal, each frequency can be output bymerely changing the setting of frequency data (phase difference data) tothe NCO of the local oscillator 70. Therefore, a data setting time of acontroller that controls the transmitter can be reduced compared with aconventional transmitter and the frequency data to the NCO can becomputed in a simpler manner.

[0163] As described above, the NCO of the first embodiment uses thenearest integer of M, where M=Fs/FD×K/L, on the assumption that Fs is asampling frequency of an output signal from the NCO, FD is the upperlimit of a desired frequency setting interval of the output signal and Kand L are arbitrary integers. The phase calculator 1 b generates phasedata by performing a modulo operation taking the integral M as a moduluswith respect to input phase difference data and phase data from thephase register 1 a. The ROM 2 stores a phase/amplitude conversion tableincluding M amplitude data and outputs amplitude data corresponding tothe generated phase data through its data terminal. Therefore, it ispossible to realize a low-spurious NCO which provides its output signalset to a frequency setting interval of a dF step, where dF=FD/K×L.

[0164] Therefore, because a low-spurious NCO, which provides its outputsignal set to a frequency setting interval lower than or equal to adesired frequency setting interval is realized on the basis of onlylow-capacity, amplitude data of M number that is smaller than aconventional one, it can be reduced in power consumption and cost.

[0165] Further, it is possible to realize the digital down-converter,the digital up-converter, the receiver with the demodulator, and thetransmitter with the modulator of the second to eighth embodiments usingthe NCO of the first embodiment. As a result, the digitaldown-converter, digital up-converter, receiver, or transmitter can bereduced in power consumption and cost compared with a conventional one.

[0166] As apparent from the above description, if the upper limit of adesired frequency setting interval of an output signal is FD, and K andL are arbitrary integers, a phase accumulator generates phase data byaccumulating input phase difference data by a modulo operation takingthe nearest integer of M as a modulus, where M=Fs/FD×K/L, and outputsthe generated phase data as an address input to a phase/amplitudeconversion table. As a result, the phase/amplitude conversion tableoutputs amplitude data corresponding to the input phase data as anoutput signal of the NCO set to a frequency setting interval of a dFstep, where dF=FD/K×L.

[0167] Therefore, a low-spurious NCO, which provides its output signalset to a frequency setting interval lower than or equal to a desiredfrequency setting interval, can be realized on the basis of onlylow-capacity, amplitude data of M number that is smaller than aconventional one, so it can be reduced in power consumption and cost.

[0168] According to a digital down-converter of the present invention, afrequency converter frequency-converts an input signal using a frequencysignal output from the NCO of claim 1 as a local oscillator and set to afrequency setting interval of a dF step, where dF=FD/K×L. In the casewhere a desired frequency setting interval FD of the input signal ishigher than or equal to a frequency setting interval dF of the frequencyconverter and is evenly divisible by it, the digital down-converter canconvert the frequency of the input signal input thereto at the frequencysetting interval FD into a desired frequency within the range of anallowable frequency deviation.

[0169] Therefore, the use of the low-spurious NCO which is realized onthe basis of only low-capacity, amplitude data of M number that issmaller than a conventional one, where M=Fs/FD×K/L, and provides itsoutput signal set to a frequency setting interval lower than or equal toa desired frequency setting interval can reduce power consumption andcost of the digital down-converter that can convert the frequency of theinput signal input thereto at the desired frequency setting intervalinto a desired frequency within the range of an allowable frequencydeviation.

[0170] According to an alternative digital down-converter of the presentinvention, one of two frequency converters provided for frequencyconversions includes a low-spurious NCO which is realized on the basisof only M1 low-capacity amplitude data and provides its output signalset to a frequency setting interval lower than or equal to a desiredfrequency setting interval, and the other includes a low-spurious NCOwhich is realized on the basis of only M2 low-capacity amplitude dataand provides its output signal set to a frequency setting interval lowerthan or equal to a desired frequency setting interval. The digitaldown-converter is able to cope with the case where a frequency settinginterval FD of an input signal is above a frequency setting interval FD1of the first frequency converter and is indivisible by it, the casewhere the frequency setting interval FD is below the frequency settinginterval FD1 and FD1 is indivisible by FD, and the case where thefrequency setting interval FD is higher than or equal to the frequencysetting interval FD1 and is evenly divisible by it, or FD is lower thanFD1 and FD1 is evenly divisible by FD, respectively.

[0171] Therefore, the use of the two low-spurious NCOs which arerealized on the basis of only low-capacity, amplitude data of M1 and M2numbers that are each smaller than a conventional one and provide theiroutput signals each set to a frequency setting interval lower than orequal to a desired frequency setting interval can reduce powerconsumption and cost of the digital down-converter that can convert thefrequency of the input signal input thereto at the desired frequencysetting interval into a desired frequency within the range of anallowable frequency deviation.

[0172] According to yet another digital down-converter of the presentinvention, in the case where a multiple of the frequency settinginterval FD1 of the first frequency converter is equal to that of thefrequency setting interval FD of the input signal, the digitaldown-converter can convert the frequency of the input signal inputthereto at the frequency setting interval FD into a desired frequencywithin the range of an allowable frequency deviation by means of onlythe first frequency converter.

[0173] Therefore, it is possible to reduce power consumption of thedigital down-converter that can convert the frequency of the inputsignal input thereto at the desired frequency setting interval into adesired frequency within the range of an allowable frequency deviation.

[0174] According to another embodiment of a digital up-converter of thepresent invention, a frequency converter frequency-converts an inputsignal using a frequency signal output from the NCO of claim 1 as alocal oscillator and set to a frequency setting interval of a dF step,where dF=FD/K×L. In the case where a desired frequency setting intervalFD of an output signal is higher than or equal to a frequency settinginterval dF of the frequency converter and is evenly divisible by it,the digital up-converter can set the frequency setting interval of itsoutput signal to FD.

[0175] Therefore, the use of the low-spurious NCO which is realized onthe basis of only low-capacity, amplitude data of M number that issmaller than a conventional one, where M=Fs/FD×K/L, and provides itsoutput signal set to a frequency setting interval lower than or equal toa desired frequency setting interval can reduce power consumption andcost of the digital up-converter that can output a signal of the desiredfrequency setting interval.

[0176] According to alternative digital up-converters of the presentinvention, one of two frequency converters provided for frequencyconversions includes a low-spurious NCO which is realized on the basisof only M1 low-capacity amplitude data and provides its output signalset to a frequency setting interval lower than or equal to a desiredfrequency setting interval, and the other includes a low-spurious NCOwhich is realized on the basis of only M2 low-capacity amplitude dataand provides its output signal set to a frequency setting interval lowerthan or equal to a desired frequency setting interval. The digitalup-converter is able to cope with the case where a frequency settinginterval FD of an output signal is above a frequency setting intervalFD2 of the second frequency converter and is indivisible by it, the casewhere the frequency setting interval FD is below the frequency settinginterval FD2 and FD2 is indivisible by FD, and the case where thefrequency setting interval FD is higher than or equal to the frequencysetting interval FD2 and is evenly divisible by it, or FD is lower thanFD2 and FD2 is evenly divisible by FD, respectively.

[0177] Therefore, the use of the two low-spurious NCOs which arerealized on the basis of only low-capacity, amplitude data of M1 and M2numbers that are each smaller than a conventional one and provide theiroutput signals each set to a frequency setting interval lower than orequal to a desired frequency setting interval can reduce powerconsumption and cost of the digital up-converter that can output asignal of the desired frequency setting interval.

[0178] According to a digital up-converter of the present invention, inthe case where a multiple of the frequency setting interval FD2 of thesecond frequency converter is equal to that of the frequency settinginterval FD of the output signal, the digital up-converter can set thefrequency setting interval of its output signal to FD by means of onlythe second frequency converter.

[0179] Therefore, it is possible to reduce power consumption of thedigital up-converter that can output a signal of the desired frequencysetting interval.

[0180] According to the preferred embodiments of the receiver of thepresent invention, one of two frequency converters provided forfrequency conversion of a received signal into an input signal desiredby a demodulator includes a low-spurious NCO which is realized on thebasis of only M1 low-capacity amplitude data and provides its outputsignal set to a frequency setting interval lower than or equal to adesired frequency setting interval, and the other includes alow-spurious NCO which is realized on the basis of only M2 low-capacityamplitude data and provides its output signal set to a frequency settinginterval lower than or equal to a desired frequency setting interval.The receiver is able to cope with the case where a frequency settinginterval FD of an input signal is above a frequency setting interval FDPof the first frequency converter and is indivisible by it, the casewhere the frequency setting interval FD is below the frequency settinginterval FDP and FDP is indivisible by FD, and the case where thefrequency setting interval FD is higher than or equal to the frequencysetting interval FDP and is evenly divisible by it, or FD is lower thanFDP and FDP is evenly divisible by FD, respectively.

[0181] Therefore, the use of the two low-spurious NCOs which arerealized on the basis of only low-capacity, amplitude data of M1 and M2numbers that are each smaller than a conventional one and provide theiroutput signals each set to a frequency setting interval lower than orequal to a desired frequency setting interval can reduce powerconsumption and cost of the receiver that can accurately convert thefrequency of the received signal input thereto at the frequency settinginterval FD into that desired by the demodulator.

[0182] According to an alternate embodiment of the receiver of thepresent invention, in the case where a multiple of the frequency settinginterval FD1 of the first frequency converter is equal to that of thefrequency setting interval FD of the received signal, the receiver canaccurately convert the frequency of the received signal input thereto atthe frequency setting interval FD into that desired by the demodulatorby means of only the first frequency converter.

[0183] Therefore, it is possible to reduce power consumption of thereceiver that can accurately convert the frequency of the receivedsignal input thereto at the frequency setting interval FD into thatdesired by the demodulator.

[0184] According to preferred embodiments of a transmitter of thepresent invention, one of two frequency converters provided forfrequency conversion of a transmit signal from a modulator into a targetfrequency includes a low-spurious NCO which is realized on the basis ofonly M1 low-capacity amplitude data and provides its output signal setto a frequency setting interval lower than or equal to a desiredfrequency setting interval, and the other includes a low-spurious NCOwhich is realized on the basis of only M2 low-capacity amplitude dataand provides its output signal set to a frequency setting interval lowerthan or equal to a desired frequency setting interval. The transmitteris able to cope with the case where a frequency setting interval FD ofan output signal is above a frequency setting interval FDP of the secondfrequency converter and is indivisible by it, the case where thefrequency setting interval FD is below the frequency setting intervalFDP and FDP is indivisible by FD, and the case where the frequencysetting interval FD is higher than or equal to the frequency settinginterval FDP and is evenly divisible by it, or FD is lower than FDP andFDP is evenly divisible by FD, respectively.

[0185] Therefore, the use of the two low-spurious NCOs which arerealized on the basis of only low-capacity, amplitude data of M1 and M2numbers that are each smaller than a conventional one and provide theiroutput signals each set to a frequency setting interval lower than orequal to a desired frequency setting interval can reduce powerconsumption and cost of the transmitter that can accurately convert thefrequency of the baseband transmit signal from the modulator into atarget transmit signal frequency.

[0186] According to an alternative embodiment transmitter of the presentinvention, in the case where a multiple of the frequency settinginterval FD2 of the second frequency converter is equal to that of thefrequency setting interval FD of the transmit signal, the transmittercan accurately convert the frequency of the baseband transmit signalfrom the modulator into that of a target transmit signal by means ofonly the second frequency converter.

[0187] Therefore, it is possible to reduce power consumption of thetransmitter that can accurately convert the frequency of the basebandtransmit signal from the modulator into a target transmit signalfrequency.

[0188] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A numerical control oscillator comprising: aphase accumulator for accumulating input phase difference data togenerate phase data, said phase accumulator including a register forstoring and outputting said phase data, and a calculator for one ofadding and subtracting said input phase difference data and said phasedata from said register; and a memory for storing a phase/amplitudeconversion table to output amplitude data corresponding to said phasedata generated by said phase accumulator, said numerical controloscillator outputting a signal of a sampling frequency Fs, wherein: ifan upper limit of a desired frequency setting interval of an outputsignal is FD and, K and L are arbitrary integers, said calculator ofsaid phase accumulator is performs one of adding and subtracting saidinput phase difference data and said phase data from said register by amodulo operation taking a nearest integer of M as a modulus, whereM=Fs/FD×K/L; and said phase/amplitude conversion table outputs a signalset to a frequency setting interval of a dF step, where dF=FD/K×L.
 2. Adigital down-converter comprising a frequency converter, the frequencyconverter including a numerical control oscillator as a local oscillatorand serving to frequency-convert an input signal sampled at a samplingfrequency Fs, said digital down-converter converting and outputting saidinput signal into an output signal with a frequency lower than that ofsaid input signal, said numerical control oscillator having: a phaseaccumulator for accumulating input phase difference data to generatephase data, said phase accumulator including a register for storing andoutputting said phase data, and a calculator for one of adding andsubtracting said input phase difference data and said phase data fromsaid register; and a memory for storing a phase/amplitude conversiontable to output amplitude data corresponding to said phase datagenerated by said phase accumulator, said numerical control oscillatoroutputting a signal of the sampling frequency Fs, wherein, if a desiredfrequency setting interval of said input signal is FD and K and L arearbitrary integers, said frequency converter is adapted tofrequency-convert said input signal using a specific signal output fromsaid local oscillator and set to a frequency setting interval of a dFstep, where dF=FD/K×L, said local oscillator outputting the specificsignal by accumulating said phase difference data by a modulo operationtaking a nearest integer of M as a modulus, where M=Fs/FD×K/L.
 3. Adigital down-converter comprising a first frequency converter, the firstfrequency converter including a numerical control oscillator as a firstlocal oscillator and serving to frequency-convert an input signalsampled at a sampling frequency Fs1, and a second frequency converter,the second frequency converter including an identical numerical controloscillator as included in the first frequency converter as a secondlocal oscillator and serving to secondarily frequency-convert an outputsignal from said first frequency converter, said digital down-converterconverting and outputting said input signal into an output signal with afrequency lower than that of said input signal by two frequencyconversions, said numerical control oscillator having: a phaseaccumulator for accumulating input phase difference data to generatephase data, said phase accumulator including a register for storing andoutputting said phase data, and a calculator for one of adding andsubtracting said input phase difference data and said phase data fromsaid register; and a memory for storing a phase/amplitude conversiontable to output amplitude data corresponding to said phase datagenerated by said phase accumulator, said numerical control oscillatoroutputting a signal of the sampling frequency, wherein: if a desiredfrequency setting interval of said input signal is FD and K1, K2 and L1are arbitrary integers, said first frequency converter is adapted tofrequency-convert said input signal using a first specific signal outputfrom said first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1×L1, said first local oscillatoroutputting the first specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1/L1; and said second frequency converter isadapted to, if a sampling frequency of the output signal from said firstfrequency converter is Fs2, frequency-convert said output signal fromsaid first frequency converter using a second specific signal outputfrom said second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=(FD mod FD1)/K2, said second localoscillator outputting the second specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs2/(FD mod FD1)×K2.
 4. The digitaldown-converter as set forth in claim 3, wherein said second frequencyconverter is adapted to stop the frequency conversion.
 5. A digitaldown-converter comprising a first frequency converter, the firstfrequency converter including a numerical control oscillator as a firstlocal oscillator and serving to frequency-convert an input signalsampled at a sampling frequency Fs1, and a second frequency converter,the second frequency converter including an identical numerical controloscillator as the first frequency converter as a second local oscillatorand serving to secondarily frequency-convert an output signal from saidfirst frequency converter, said digital down-converter converting andoutputting said input signal into an output signal with a frequencylower than that of said input signal by two frequency conversions, saidnumerical control oscillator having: a phase accumulator foraccumulating input phase difference data to generate phase data, saidphase accumulator including a register for storing and outputting saidphase data, and a calculator for one of adding and subtracting saidinput phase difference data and said phase data from said register; anda memory for storing a phase/amplitude conversion table to outputamplitude data corresponding to said phase data generated by said phaseaccumulator, said numerical control oscillator outputting a signal ofthe sampling frequency, wherein: if a desired frequency setting intervalof said input signal is FD, and K1, K2 and L1 are arbitrary integers,said first frequency converter is adapted to frequency-convert saidinput signal using a first specific signal output from said first localoscillator and set to a frequency setting interval of an FD1 step, whereFD1=FD/K1×L1, said first local oscillator outputting the first specificsignal by accumulating said phase difference data by a modulo operationtaking a nearest integer of M1 as a modulus, where M1=Fs1/FD×K1/L1; andsaid second frequency converter is adapted to, if a sampling frequencyof the output signal from said first frequency converter is Fs2,frequency-convert said output signal from said first frequency converterusing a second specific signal output from said second local oscillatorand set to a frequency setting interval of an FD2 step, where FD2=(FD1mod FD)/K2, said second local oscillator outputting the second specificsignal by accumulating said phase difference data by a modulo operationtaking a nearest integer of M2 as a modulus, where M2=Fs2/(FD1 modFD)×K2.
 6. The digital down-converter as set forth in claim 5, whereinsaid second frequency converter is adapted to stop the frequencyconversion.
 7. A digital down-converter comprising a first frequencyconverter, the first frequency converter including a numerical controloscillator as a first local oscillator and serving to frequency-convertan input signal sampled at a sampling frequency Fs1, and a secondfrequency converter, the second frequency converter including anidentical numerical control oscillator as in the first frequencyconverter as a second local oscillator and serving to secondarilyfrequency-convert an output signal from said first frequency converter,said digital down-converter converting and outputting said input signalinto an output signal with a frequency lower than that of said inputsignal by two frequency conversions, said numerical control oscillatorhaving: a phase accumulator for accumulating input phase difference datato generate phase data, said phase accumulator including a register forstoring and outputting said phase data, and a calculator for one ofadding and subtracting said input phase difference data and said phasedata from said register; and a memory for storing a phase/amplitudeconversion table to output amplitude data corresponding to said phasedata generated by said phase accumulator, said numerical controloscillator outputting a signal of the sampling frequency, wherein: if adesired frequency setting interval of said input signal is FD and K1, K2and L1 are arbitrary integers, said first frequency converter is adaptedto frequency-convert said input signal using a first specific signaloutput from said first local oscillator and set to a frequency settinginterval of an FD1 step, where FD1=FD/K1×L1, said first local oscillatoroutputting the first specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1/L1; and said second frequency converter isadapted to, if a sampling frequency of the output signal from said firstfrequency converter is Fs2, frequency-convert said output signal fromsaid first frequency converter using a second specific signal outputfrom said second local oscillator and set to a frequency settinginterval of an FD2 step, where FD2=FD/K2, said second local oscillatoroutputting the second specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs2/FD×K2.
 8. The digital down-converter as setforth in claim 7, wherein said second frequency converter is adapted tostop the frequency conversion.
 9. A digital up-converter comprising afrequency converter, the frequency converter including a numericalcontrol oscillator as a local oscillator and serving tofrequency-convert an input signal, said digital up-converter convertingsaid input signal into a signal with a frequency higher than that ofsaid input signal and outputting the converted signal as an outputsignal sampled at a sampling frequency Fs, said numerical controloscillator having: a phase accumulator for accumulating input phasedifference data to generate phase data, said phase accumulator includinga register for storing and outputting said phase data, and a calculatorfor one of adding and subtracting said input phase difference data andsaid phase data from said register; and a memory for storing aphase/amplitude conversion table to output amplitude data correspondingto said phase data generated by said phase accumulator, said numericalcontrol oscillator outputting a signal of the sampling frequency Fs,wherein, if a desired frequency setting interval of said output signalis FD and K and L are arbitrary integers, said frequency converter isadapted to frequency-convert said input signal using a specific signaloutput from said local oscillator and set to a frequency settinginterval of a dF step, where dF=FD/K×L, said local oscillator outputtingthe specific signal by accumulating said phase difference data by amodulo operation taking a nearest integer of M as a modulus, whereM=Fs/FD×K/L.
 10. A digital up-converter comprising a first frequencyconverter, the first frequency converter including a numerical controloscillator as a first local oscillator and serving to frequency-convertan input signal, and a second frequency converter, the second frequencyconverter including an identical numerical control oscillator asincluded in the first frequency converter as a second local oscillatorand serving to secondarily frequency-convert an output signal from saidfirst frequency converter, said digital up-converter performing twofrequency conversions to convert said input signal into a signal with afrequency higher than that of said input signal and output the convertedsignal as an output signal sampled at a sampling frequency Fs2, saidnumerical control oscillator having: a phase accumulator foraccumulating input phase difference data to generate phase data, saidphase accumulator including a register for storing and outputting saidphase data, and a calculator for one of adding and subtracting saidinput phase difference data and said phase data from said register; anda memory for storing a phase/amplitude conversion table to outputamplitude data corresponding to said phase data generated by said phaseaccumulator, said numerical control oscillator outputting a signal ofthe sampling frequency, wherein: if a desired frequency setting intervalof said output signal is FD, and K1, K2, and L2 are arbitrary integers,said second frequency converter is adapted to frequency-convert theoutput signal from said first frequency converter using a first specificsignal output from said second local oscillator and set to a frequencysetting interval of an FD2 step, where FD2=FD/K2×L2, said second localoscillator outputting the first specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs2/FD×K2/L2; and said first frequencyconverter is adapted to, if a sampling frequency of said input signal isFs1, frequency-convert said input signal using a second specific signaloutput from said first local oscillator and set to a frequency settinginterval of an FD1 step, where FD1=(FD mod FD2)/K1, said first localoscillator outputting the second specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM1 as a modulus, where M1=Fs1/(FD mod FD2)×K1.
 11. The digitalup-converter as set forth in claim 10, wherein said first frequencyconverter is adapted to stop the frequency conversion.
 12. A digitalup-converter comprising a first frequency converter, the first frequencyconverter including a numerical control oscillator as a first localoscillator and serving to frequency-convert an input signal, and asecond frequency converter, the second frequency converter including anidentical numerical control oscillator as included in the firstfrequency converter as a second local oscillator and serving tosecondarily frequency-convert an output signal from said first frequencyconverter, said digital up-converter performing two frequencyconversions to convert said input signal into a signal with a frequencyhigher than that of said input signal and output the converted signal asan output signal sampled at a sampling frequency Fs2, said numericalcontrol oscillator having: a phase accumulator for accumulating inputphase difference data to generate phase data, said phase accumulatorincluding a register for storing and outputting said phase data, and acalculator for one of adding and subtracting said input phase differencedata and said phase data from said register; and a memory for storing aphase/amplitude conversion table to output amplitude data correspondingto said phase data generated by said phase accumulator, said numericalcontrol oscillator outputting a signal of the sampling frequency,wherein: if a desired frequency setting interval of said output signalis FD and K1, K2 and L2 are arbitrary integers, said second frequencyconverter is adapted to frequency-convert the output signal from saidfirst frequency converter using a first specific signal output from saidsecond local oscillator and set to a frequency setting interval of anFD2 step, where FD2=FD/K2×L2, said second local oscillator outputtingthe first specific signal by accumulating said phase difference data bya modulo operation taking a nearest integer of M2 as a modulus, whereM2=Fs2/FD×K2/L2; and said first frequency converter is adapted to, if asampling frequency of said input signal is Fs1, frequency-convert saidinput signal using a second specific signal output from said first localoscillator and set to a frequency setting interval of an FD1 step, whereFD1=(FD2 mod FD)/K1, said first local oscillator outputting the secondspecific signal by accumulating said phase difference data by a modulooperation taking a nearest integer of M1 as a modulus, where M1=Fs1/(FD2mod FD)×K1.
 13. The digital up-converter as set forth in claim 12,wherein said first frequency converter is adapted to stop the frequencyconversion.
 14. A digital up-converter comprising a first frequencyconverter, the first frequency converter including a numerical controloscillator as a first local oscillator and serving to frequency-convertan input signal, and a second frequency converter, the second frequencyconverter including an identical numerical control oscillator asincluded in the first frequency converter as a second local oscillatorand serving to secondarily frequency-convert an output signal from saidfirst frequency converter, said digital up-converter performing twofrequency conversions to convert said input signal into a signal with afrequency higher than that of said input signal and output the convertedsignal as an output signal sampled at a sampling frequency Fs2, saidnumerical control oscillator having: a phase accumulator foraccumulating input phase difference data to generate phase data, saidphase accumulator including a register for storing and outputting saidphase data, and a calculator for one of adding and subtracting saidinput phase difference data and said phase data from said register; anda memory for storing a phase/amplitude conversion table to outputamplitude data corresponding to said phase data generated by said phaseaccumulator, said numerical control oscillator outputting a signal ofthe sampling frequency, wherein: if a desired frequency setting intervalof said output signal is FD and K1, K2 and L2 are arbitrary integers,said second frequency converter is adapted to frequency-convert theoutput signal from said first frequency converter using a first specificsignal output from said second local oscillator and set to a frequencysetting interval of an FD2 step, where FD2=FD/K2×L2, said second localoscillator outputting the first specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM2 as a modulus, where M2=Fs2/FD×K2/L2; and said first frequencyconverter is adapted to, if a sampling frequency of said input signal isFs1, frequency-convert said input signal using a second specific signaloutput from said first local oscillator and set to a frequency settinginterval of an FD1 step, where FD1=FD/K1, said first local oscillatoroutputting the second specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/FD×K1.
 15. The digital up-converter as set forthin claim 14, wherein said first frequency converter is adapted to stopthe frequency conversion.
 16. A receiver comprising a first frequencyconverter, the first frequency converter including a first localoscillator and serving to frequency-convert a received signal, saidfirst local oscillator including a numerical control oscillatoroperating at a sampling frequency Fs and a phase locked loop (PLL)circuit having a multiplication ratio P (P is an integer) and acting toreceive the output signal from the numerical control oscillator as areference signal, a second frequency converter, the second frequencyconverter including an identical numerical control oscillator asincluded in the first local oscillator as a second local oscillator andserving to secondarily frequency-convert an output signal from saidfirst frequency converter, and a demodulator for demodulating an outputsignal from said second frequency converter to extract received datatherefrom, said receiver converting said received signal into a basebandreceived signal with a frequency lower than that of said received signalby two frequency conversions and extracting the received data from theconverted baseband received signal, said numerical control oscillatorhaving: a phase accumulator for accumulating input phase difference datato generate phase data, said phase accumulator including a register forstoring and outputting said phase data, and a calculator for one ofadding and subtracting said input phase difference data and said phasedata from said register; and a memory for storing a phase/amplitudeconversion table to output amplitude data corresponding to said phasedata generated by said phase accumulator, said numerical controloscillator outputting a signal of the sampling frequency, wherein: if adesired frequency setting interval of said received signal is FD and K1,K2 and L1 are arbitrary integers, said first frequency converter isadapted to frequency-convert said received signal using a first specificsignal output from said first local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K1×L1, said first localoscillator outputting the first specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM1 as a modulus, where M1=Fs/FD×K1/L1×P; and said second frequencyconverter is adapted to, if a sampling frequency of the output signalfrom said first frequency converter is Fs1, frequency-convert saidoutput signal from said first frequency converter using a secondspecific signal output from said second local oscillator and set to afrequency setting interval of an FD2 step, where FD2=(FD mod FDP)/K2,said second local oscillator outputting the second specific signal byaccumulating said phase difference data by a modulo operation taking anearest integer of M2 as a modulus, where M2=Fs1/(FD mod FDP)×K2. 17.The receiver as set forth in claim 16, wherein said second frequencyconverter is adapted to stop the frequency conversion.
 18. A receivercomprising a first frequency converter including a first localoscillator and serving to frequency-convert a received signal, saidfirst local oscillator including a numerical control oscillatoroperating at a sampling frequency Fs and a PLL circuit having amultiplication ratio P (P is an integer) and acting to receive theoutput signal from the numerical control oscillator as a referencesignal, a second frequency converter including an identical numericalcontrol oscillator as included in the first local oscillator as a secondlocal oscillator and serving to secondarily frequency-convert an outputsignal from said first frequency converter, and a demodulator fordemodulating an output signal from said second frequency converter toextract received data therefrom, said receiver converting said receivedsignal into a baseband received signal with a frequency lower than thatof said received signal by two frequency conversions and extracting thereceived data from the converted baseband received signal, saidnumerical control oscillator having: a phase accumulator foraccumulating input phase difference data to generate phase data, saidphase accumulator including a register for storing and outputting saidphase data, and a calculator for one of adding and subtracting saidinput phase difference data and said phase data from said register; anda memory for storing a phase/amplitude conversion table to outputamplitude data corresponding to said phase data generated by said phaseaccumulator, said numerical control oscillator outputting a signal ofthe sampling frequency, wherein: if a desired frequency setting intervalof said received signal is FD, and K1, K2, and L1 are arbitraryintegers, said first frequency converter is adapted to frequency-convertsaid received signal using a first specific signal output from saidfirst local oscillator and set to a frequency setting interval of an FDPstep, where FDP=FD/K1×L1, said first local oscillator outputting thefirst specific signal by accumulating said phase difference data by amodulo operation taking a nearest integer of M1 as a modulus, whereM1=Fs/FD×K1/L1×P; and said second frequency converter is adapted to, ifa sampling frequency of the output signal from said first frequencyconverter is Fs1, frequency-convert said output signal from said firstfrequency converter using a second specific signal output from saidsecond local oscillator and set to a frequency setting interval of anFD2 step, where FD2=(FDP mod FD)/K2, said second local oscillatoroutputting the second specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M2 asa modulus, where M2=Fs1/(FDP mod FD)×K2.
 19. The receiver as set forthin claim 18, wherein said second frequency converter is adapted to stopthe frequency conversion.
 20. A receiver comprising a first frequencyconverter including a first local oscillator and serving tofrequency-convert a received signal, said first local oscillatorincluding a numerical control oscillator operating at a samplingfrequency Fs and a PLL circuit having a multiplication ratio P (P is aninteger) and acting to receive the output signal from the numericalcontrol oscillator as a reference signal, a second frequency converterincluding an identical numerical control oscillator as included in thefirst local oscillator as a second local oscillator and serving tosecondarily frequency-convert an output signal from said first frequencyconverter, and a demodulator for demodulating an output signal from saidsecond frequency converter to extract received data therefrom, saidreceiver converting said received signal into a baseband received signalwith a frequency lower than that of said received signal by twofrequency conversions and extracting the received data from theconverted baseband received signal, said numerical control oscillatorhaving: a phase accumulator for accumulating input phase difference datato generate phase data, said phase accumulator including a register forstoring and outputting said phase data, and a calculator for one ofadding and subtracting said input phase difference data and said phasedata from said register; and a memory for storing a phase/amplitudeconversion table to output amplitude data corresponding to said phasedata generated by said phase accumulator, said numerical controloscillator outputting a signal of the sampling frequency, wherein: if adesired frequency setting interval of said received signal is FD, andK1, K2, and L1 are arbitrary integers, said first frequency converter isadapted to frequency-convert said received signal using a first specificsignal output from said first local oscillator and set to a frequencysetting interval of an FDP step, where FDP=FD/K1×L1, said first localoscillator outputting the first specific signal by accumulating saidphase difference data by a modulo operation taking a nearest integer ofM1 as a modulus, where M1=Fs/FD×K1/L1×P; and said second frequencyconverter is adapted to, if a sampling frequency of the output signalfrom said first frequency converter is Fs1, frequency-convert saidoutput signal from said first frequency converter using a secondspecific signal output from said second local oscillator and set to afrequency setting interval of an FD2 step, where FD2=FD/K2, said secondlocal oscillator outputting the second specific signal by accumulatingsaid phase difference data by a modulo operation taking a nearestinteger of M2 as a modulus, where M2=Fs1/FD×K2.
 21. The receiver as setforth in claim 20, wherein said second frequency converter is adapted tostop the frequency conversion.
 22. A transmitter comprising a modulatorfor modulating and outputting a baseband transmit signal based ontransmit data, a first frequency converter including a numerical controloscillator as a first local oscillator and serving to frequency-convertthe output signal from said modulator, a second frequency converterincluding a second local oscillator and serving to secondarilyfrequency-convert an output signal from said first frequency converter,said second local oscillator including an identical numerical controloscillator as included in the first frequency converter operating at asampling frequency Fs and a PLL circuit having a multiplication ratio P(P is an integer) and acting to receive the output signal from thenumerical control oscillator as a reference signal, said transmitterconverting and outputting said baseband transmit signal into a transmitsignal with a frequency higher than that of said baseband transmitsignal by two frequency conversions, said numerical control oscillatorhaving: a phase accumulator for accumulating input phase difference datato generate phase data, said phase accumulator including a register forstoring and outputting said phase data, and a calculator for one ofadding and subtracting said input phase difference data and said phasedata from said register; and a memory for storing a phase/amplitudeconversion table to output amplitude data corresponding to said phasedata generated by said phase accumulator, said numerical controloscillator outputting a signal of the sampling frequency, wherein: if adesired frequency setting interval of said transmit signal is FD, andK1, K2, and L2 are arbitrary integers, said second frequency converteris adapted to frequency-convert the output signal from said firstfrequency converter using a first specific signal output from saidsecond local oscillator and set to a frequency setting interval of anFDP step, where FDP=FD/K2×L2, said second local oscillator outputtingthe first specific signal by accumulating said phase difference data bya modulo operation taking a nearest integer of M2 as a modulus, whereM2=Fs/FD×K2/L2×P; and said first frequency converter is adapted to, if asampling frequency of the output signal from said modulator is Fs1,frequency-convert said output signal from said modulator using a secondspecific signal output from said first local oscillator and set to afrequency setting interval of an FD1 step, where FD1=(FD mod FDP)/K1,said first local oscillator outputting the second specific signal byaccumulating said phase difference data by a modulo operation taking anearest integer of M1 as a modulus, where M1=Fs1/(FD mod FDP)×K1. 23.The transmitter as set forth in claim 22, wherein said first frequencyconverter is adapted to stop the frequency conversion.
 24. A transmittercomprising a modulator for modulating and outputting a baseband transmitsignal based on transmit data, a first frequency converter including anumerical control oscillator as a first local oscillator and serving tofrequency-convert the output signal from said modulator, a secondfrequency converter including a second local oscillator and serving tosecondarily frequency-convert an output signal from said first frequencyconverter, said second local oscillator including an identical numericalcontrol oscillator as included in the first frequency converteroperating at a sampling frequency Fs and a PLL circuit having amultiplication ratio P (P is an integer) and acting to receive theoutput signal from the numerical control oscillator as a referencesignal, said transmitter converting and outputting said basebandtransmit signal into a transmit signal with a frequency higher than thatof said baseband transmit signal by two frequency conversions, saidnumerical control oscillator having: a phase accumulator foraccumulating input phase difference data to generate phase data, saidphase accumulator including a register for storing and outputting saidphase data, and a calculator for one of adding and subtracting saidinput phase difference data and said phase data from said register; anda memory for storing a phase/amplitude conversion table to outputamplitude data corresponding to said phase data generated by said phaseaccumulator, said numerical control oscillator outputting a signal ofthe sampling frequency, wherein: if a desired frequency setting intervalof said transmit signal is FD, and K1, K2, and L2 are arbitraryintegers, said second frequency converter is adapted tofrequency-convert the output signal from said first frequency converterusing a first specific signal output from said second local oscillatorand set to a frequency setting interval of an FDP step, whereFDP=FD/K2×L2, said second local oscillator outputting the first specificsignal by accumulating said phase difference data by a modulo operationtaking a nearest integer of M2 as a modulus, where M2=Fs/FD×K2/L2×P; andsaid first frequency converter is adapted to, if a sampling frequency ofthe output signal from said modulator is Fs1, frequency-convert saidoutput signal from said modulator using a second specific signal outputfrom said first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=(FDP mod FD)/K1, said first local oscillatoroutputting the second specific signal by accumulating said phasedifference data by a modulo operation taking a nearest integer of M1 asa modulus, where M1=Fs1/(FDP mod FD)×K1.
 25. The transmitter as setforth in claim 24, wherein said first frequency converter is adapted tostop the frequency conversion.
 26. A transmitter comprising a modulatorfor modulating and outputting a baseband transmit signal based ontransmit data, a first frequency converter including a numerical controloscillator as a first local oscillator and serving to frequency-convertthe output signal from said modulator, a second frequency converterincluding a second local oscillator and serving to secondarilyfrequency-convert an output signal from said first frequency converter,said second local oscillator including an identical numerical controloscillator as included in the first frequency converter operating at asampling frequency Fs and a PLL circuit having a multiplication ratio P,where P is an integer, and acting to receive the output signal from thenumerical control oscillator of claim 1 as a reference signal, saidtransmitter converting and outputting said baseband transmit signal intoa transmit signal with a frequency higher than that of said basebandtransmit signal by two frequency conversions, wherein: if a desiredfrequency setting interval of said transmit signal is FD, and K1, K2,and L2 are arbitrary integers, said second frequency converter isadapted to frequency-convert the output signal from said first frequencyconverter using a first specific signal output from said second localoscillator and set to a frequency setting interval of an FDP step, whereFDP=FD/K2×L2, said second local oscillator outputting the first specificsignal by accumulating said phase difference data by a modulo operationtaking a nearest integer of M2 as a modulus, where M2=Fs/FD×K2/L2×P; andsaid first frequency converter is adapted to, if a sampling frequency ofthe output signal from said modulator is Fs1, frequency-convert saidoutput signal from said modulator using a second specific signal outputfrom said first local oscillator and set to a frequency setting intervalof an FD1 step, where FD1=FD/K1, said first local oscillator outputtingthe second specific signal by accumulating said phase difference data bya modulo operation taking a nearest integer of M1 as a modulus, whereM1=Fs1/FD×K1.
 27. The transmitter as set forth in claim 26, wherein saidfirst frequency converter is adapted to stop the frequency conversion.